Not Mine, Never Mine, Usual Disclaimers.
Kirk had been sufficiently distracted by attempting to scratch his back by rolling on the towel; it had worked to a certain degree. It had also prevented him from noticing Spock leave. Deciding that he might as well take full advantage of the situation and take a nap. Curling up on the blanket left of the floor, which was miraculously dry, Kirk fell asleep.
Kirk awake to discover two things: Spock hadn't come back yet, and he was really thirsty. Attempting to distract himself, Kirk decided to explore the bathroom from the viewpoint of a puppy; it wasn't as if he had taken a good look when he was a human either.
It provided a distraction for so long; there were only so many places to look at, and half of those he couldn't even reach. His gathering thirst wasn't helping; it took all the fun out of exploring. The sink was too high for him to reach, but by using the pipe as a step, he managed it. Kirk ran into his next problem, for that he had no way to turn the tap on. The next thought made him pause.
Toilets have water in them.
If he drank from the toilet, he was pretty much confirming that he was now a dog, on the other hand, he didn't really have very many options at the moment. He put it off for as long as he could stand, but eventually need won. Clambering onto the bowl was easier said than done, it was quite slippery. He thanked his lucky stars that the lid wasn't down; he never would have been able to get it up. As he bent forward, his paws slipped on the smooth surface, sending him tumbling into the toilet itself. The water tasted funny, but it sated his thirst. Getting out again was the hard part; it required several attempts and water spilt over the floor before it was successful. Once he was out, Kirk became aware of his hunger that had taken hold of his stomach, that had been growing since his last meal, which would have been lunch, hours ago.
Kirk was also lonely, there was no one around, he was seemingly forgotten, even though he didn't mind being alone normally, something about being a puppy made the loneliness upsetting. As time wore on, there was nothing to distract him; he was bored, hungry and lonely. He began scratching at the door and barking, surely Spock was in his quarters and could hear him? When it began to be painfully obvious that no one was coming, Kirk curled back up in the blanket, burying his nose into the blanket where there was an interesting smell, which he presumed was Spock, trying to ignore the well of unhappiness inside of him. Part of him felt like crying, which was ridiculous, but before he could stop himself, he was howling, which made him feel batter, but now that he had started, he didn't want to stop.