Im lost!

Question
Hey.
Um, I have a male turtle. Atleast I think it's a male because its front claws are pretty long for it's age. He's about the size of a computer mouse.
yea, anyways.. I came in my room a few days ago and it was at the bottom of the aquarium, like on the window at the bottom and it looked very concentrated. Also, it had a big black bubble that was sticking out of its tail. As soon as it saw me approach it sucked it back inside it's tail and im just concerned bc I have a female turtle that's slightly bigger and she's in the same aquarium. But everything has been alright with both of them so far so I'm not concerned about them being aggressive towards eachother. But I was wondering if they're getting ready to mate or if it's simply a health issue.
I would really appreaciate if you'd help me out with this. Oh and by the way.. they're both red ear slider tutles.
Thanks again.
Kevin.

Answer
Whenever there is even a minor glitch, I always recommend that you review a good care site, like http://www.redearslider.com and make sure the basic cares and diet are OK.

I suspect that you saw a small prolapse- part of an internal organ popping out. The fact that it pulled right back in tells me that it is not serious- we only worry about his common event if it cannot pull back in on its own.

Aggression or mating are possibilities. The signs of aggression are fighting and biting, and mating is signaled by a dance where the male strokes the female.

Both are reduced (or made less stressful) in a large-enough tank.

Good luck!