A/N: Thank you so much, mctbones, for your suggestion! It was actually very, very helpful :) And a great big thank you, also, to everyone for all your reviews and support. It means a lot and so far, I feel like I'm updating pretty regularly. I owe that directly to you guys :D Thank you!

The inability to use his left arm proved to be more bothersome than McCoy had earlier imagined. It was amazing the countless jobs the limb preformed on a regular basis without his knowledge. Unfortunately, the lab technicians had little use for a one armed man and respectfully asked that he keep out of the way.

"Don't overwork yourself, Doctor McCoy," they said pleasantly, escorting him to the door.

Now, not only did he feel guilty for the work and delay he was causing, but he also felt useless, which was more daunting than he cared to admit.

And so he let them poke and prod his arm, taking samples and conducting tests, all the while feeling like an oversized lab rat. Of course, saying he let them is a little too gracious to the doctor's temperament. He did his share of muttering and humphing, enough so to make everyone in proximity of him irritable. Uselessness did not suit him at all.

At supper, McCoy was sitting by himself, his dead arm propped up on the table. He just stared at it, thinking dull, bored thoughts. If there was one thing they had found out, it was that the life form was immaterial...taking over his tissue and cells for its own form. That then begged the question of how to get it out. Presently, everyone was at a loss.

"How're you feeling, Bones?"

McCoy startled and looked up to see the captain taking a seat across from him. McCoy shrugged and sighed. "No better, no worse." He smiled sadly. "I suppose that's a good thing, huh?"

"Depends." Kirk tilted his head. "Any developments on how to get rid of the life form?"

"No. It's become part of me. I've been wracking my brain over it all day, but...nothing. I can think of absolutely nothing." His fingers started drumming the table.

Kirk looked at them thoughtfully. "I thought you couldn't move that arm...at all."

"I can't, I-" McCoy stopped cold when he saw his fingers moving of their own accord. "I'm not doing that, Jim."

"It's the creature?" Kirk asked in a hoarse whisper, as if the lifeform could hear him.

McCoy nodded dumbly, watching with queer fascination as his fist clenched and then opened, spreading his fingers wide and closing them again.

"It's like," McCoy said quietly, "whatever it is, is testing its abilities."

"We'd better get you down to sickbay," Kirk said, standing up and reaching out to take McCoy's other arm.

McCoy shrugged him off with a forced smile. "It's just an arm, Jim, I can still walk." He stood as he spoke, as if to prove it.

"I know, but..." Kirk faltered, then he sighed. "Yes, I suppose you're right."

The two of them walked to Sickbay in silence, McCoy all too aware that his left hand was preforming its own tasks, clutching and stretching too deliberately for comfort. It made the pit of his stomach knot.

"Fascinating."

McCoy glowered. "Really, Spock. That's all you have to say about it?"

The Vulcan regarded the doctor with a deadpan stare. "To be perfectly frank, doctor, yes."

"The question is, what do we do about it?" Kirk was leaning against McCoy's desk, arms crossed.

"Continue our efforts to extract creature," Spock said, "As of yet, I do not see the creature's ability to use the doctor's hand a threat."

"Be that as it may," McCoy said irritably, because he hated to say it, "I find the entire thing unnerving."

Spock raised an eyebrow. "We might try sedating the creature if it troubles you that much."

"Well, I'd like to see your reaction to a creature taking posession of one of your appendages," McCoy grumbled.

"May I remind you, doctor, that I have had such an experience with the exception that it was my entire body that which the creature possessed."

McCoy knew when he was beat, even if he didn't like it. "Ah, hum," he acknowledged after a moment's hesitation.

After having Nurse Chapel adminster a small dose of sedative to his arm, his hand slowly stopped moving, much to McCoy's relief.

A/N: Next chapter coming soon...