His body is losing the ability to regulate temperature.
The metal arm remains cool to the touch. The Soldier cannot recall it ever feeling warm. His arm has some process that keeps it from overheating, that keeps the warmth from the rest of his body at bay. And his body is warm. Generally, he thinks, the heat is controlled through the leaking of fluids and salt through the skin, which is what had been happening during the walk into Brooklyn and the day prior. But that process has suddenly ceased.
He's never needed to perform maintenance on himself before. HYDRA was always there to provide it. He cannot, replaying what little memories he has of HYDRA attending to him, determine how to emulate the upkeep. Everything was provided in tubes and syringes. He remembers injections when he would come out of the cold, substances that made the shivering stop and helped restore him to full functioning.
Once he was restored they would switch to the tubes, clear plastic lines that carried everything in and out of his body. Whatever fluids they hooked up to the tubes were also clear, whether it was the small injections into the line that halted his consciousness or the bags that dripped substances into the tubes for hours. He has access to none of that and he is not sure he could place an intravenous line without causing an embolism even if he did have the necessary tools.
It has barely been twenty-four hours since he left the care of HYDRA and already he is beginning to break down.
The English voice, the one that wanted so badly to be a person, has no suggestion for how to keep the body functioning. It only returns to water, over and over again, and water brings to mind Steve, unconscious and wounded, the water from the Potomac leaking from his mouth. It makes the Soldier think of injuring Steve, of how they could have drowned together and how his body would not be malfunctioning. He refuses to dwell and dismisses it.
Heat is not unlike pain. There is pain as well—something is happening in his throat that he thinks is called soreness—but he can continue without letting either sensation delay him, so he does. His body may adjust. Even if it does not, so long as the experience does not escalate, he can function around it. He will have to readjust his plans, expend less energy than he could if functioning at full capacity, but he will manage.
The first adjustment is not to move without the cover of darkness. There will be less exposure to the heat of the sun that way, and so less chance of elevating his own temperature. Beyond that, there will be fewer people to around to slow him, notice him, or track him. Will HYDRA have realized their asset did not go down with the helicarrier by now? The Soldier thinks it may have been stupid to come to Brooklyn straight away: the foolish, easy targets return to their homes. And while this isn't home—home is a quiet and icy tank—this is the body of James Buchanan Barnes, and this was where Barnes lived. But maybe HYDRA will not think to track a machine the way they track people.
The Soldier finds a desolate building and takes refuge within. It is not completely abandoned; he can hear others inside but they are so loud in their movements that they cannot be assassins or any sort of agents. He catches glimpses as he ascends the levels and his mind says they are vagrants, whatever vagrants may be. He takes a vantage point that allows a good view of all sides around this location, in case of ambush, and watches, waits.
He thinks he remembers more people smoking in the 1940s than he sees on the streets now. He wonders if Barnes smoked, but his fingers do not form the configuration that holds a cigarette without conscious thought, and why would Barnes smoke when he had an asthmatic friend?
Earaches, the English voice thinks, and the Soldier does not understand why. The pain is in his throat.
That sensation has intensified by nightfall, though he has been careful to do nothing to further exacerbate it. Has he become sick? Perhaps without the injections from his doctors, his immune system does not function. Perhaps he swallowed some contaminant or bacteria from the Potomac, and that is why the word "water" is repeating in his mind.
The building where the Internet said James Buchanan Barnes had lived has been razed and replaced with another. He could break in, but what point would there be? If standing in a specific location could restore memories, then he would be Barnes by now.
Barnes might know how to fix the pain in his throat. He thinks, from the light in Barnes's face in the Smithsonian footage, that Barnes was good at being human.
It takes far longer than it should to reach the building where Steve had lived. The Soldier had not realized he was capable of becoming lost until it had already happened. He will turn a corner only to find it is the opposite of the one he intended, and will then double back only to find himself in an entirely new location. He feels vertigo and his heart does not beat in rhythm. It speeds up and seems to thump more times than it should.
He feels fatigued, the way his body reacts after HYDRA administers the injections that put him to sleep. His head is aching in time with the broken rhythm of his pulse, and when he turns another corner and finds himself looking at Steve, it takes a full five seconds before he reacts.
Steve looks just as he did on the helicarrier, bruised and cut. The stain from the gunshot to the stomach is vivid and dripping. The Soldier knows this isn't possible—even with the effects of the serum he read about, Steve should not be here and standing, not after a day—but the plausibility is of no consequence, because it is happening.
Steve opens his mouth and the Soldier runs.
He is panting even though he has barely begun to move, mind simultaneously whirling and dragging. Steve has found him, but he is a weapon now, an assassin, the thing that Steve stops.
[No he wouldn't fight me he said]
If they aren't going to fight then Steve must want him as a weapon, because the Soldier possesses no other value, but he can't be an effective weapon around Steve, he'll malfunction and then he'll be thrown away. Or else Steve will want him to be human, to be Barnes, and he can't be that man and a day of humanity is already killing him.
The Soldier trips. Over his own feet, from the feel of it. He does not have time to look down before his body is striking the pavement and skin is scraping as he slides to a stop, rolling off of the sidewalk and into the gutter. A water bottle, discarded and half-emptied, rolls against the grating by his head. He pushes himself with one scratched hand and one metal one, until he is on his knees. His hands brace against the asphalt, prepared to push off and run.
"Стоп."
He does not fully stop at the order, glancing over his shoulder.
Steve has returned. But not the Steve that he just saw, the one with the bullet in his stomach. This is the small Steve, the fragile body in the Smithsonian's pre-serum photo. It's impossible but the Soldier's head is reeling, his throat feels as if he's been stabbed, and his tongue seems too large for his mouth, and Steve being shorter is strangely not strange in this circumstance.
"Я думал, ты выше," the Soldier mutters, words hardly coherent, the skin of his lips cracking. He realizes he spoke without prompting and prepares himself to be struck. He does not think this Steve will have much in the way of striking force, but he thinks it will still hurt badly.
Steve does not approach him, pointing past the Soldier's body. "Пей," he orders, and the voice is familiar, but he does not recognize it as Steve's. Maybe Steve sounds different in Russian.
The Soldier stares, confused, and Steve advances, points again, and he sees the water bottle and sees Steve's hand, a hand he cannot feel, brush against his flushed face. "Ты горишь, дорогой. Пей."
He takes the water bottle from the gutter, twists the lid, sips. He cannot recall ever drinking, but his body—Barnes's body—seems to know what to do. Was water the fluid in HYDRA's tubes? He drinks until the bottle is empty. "Ты мой хозяин?" he asks. Steve is giving the instructions now, and Steve was Barnes's commanding officer. Steve knows how to be a human. It makes sense for Steve to be his handler. He thinks he will be safe that way. He thinks his mind will be quiet.
There is an impact in his chest, reverberating through him, but Steve has not told him to feel anything and so he ignores it. His eyes are warm, and the metal hand wipes at them instinctively, but there is nothing there to clear away. Why should he want autonomy now? He has never needed it before. He will be better off without it.
Steve does not answer, neither in the affirmative nor the negative. Instead, he glances at the empty bottle. "Пей больше," he orders, "пока боль не утихнет."
The Soldier stands, walks. He must find more to drink more, and once he has done so he will return. He will let Steve lead him, no matter what Steve's appearance, to whatever location Steve desires him to be in. He will follow his orders, serve and shelter him, and he will learn to be content.
But when he returns, stomach full of water and body no longer on the verge of collapse, Steve is gone.
A/N: I couldn't find any solid resources on if hallucinations begin on the second or third day of dehydration, but considering that injuries also contribute to dehydration and Bucky was badly injured from the helicarrier stuff before his healing factor kicked in (in fact, for all I know the healing factor could also contribute), so hallucinations in the second day of dehydration didn't seem like too much of a stretch.
Earaches: There's an old folk remedy which persists to this day that blowing pipe or tobacco smoke into another's ear will cure an earache. Which is the sort of thing I could see Bucky doing for Steve during a cold.
Translations for the Russian are as follows:
Стоп = Stop
Я думал, ты выше = I thought you were taller
Пей = Drink
Ты горишь, дорогой. Пей. = You're burning up, dear. Drink.
Ты мой хозяин? = You are my master?
Пей больше, пока боль не утихнет. = Drink more, drink until the pain stops.