I was driving down the road one day, when I saw the familer little stride of a box turle. (later found out to be an eastern box turtle) Without thinking, I took him home right away, because nobody wants a turtle hit on the road, and lucky for me, I was only a few houses from my own. Anyway, I took him in the backyard (it was a very sunny day), and put him in the pen that my red-eared slider was in. It's a fairly large pen, big enough, so that the two stood on the opposite corners, and just stared. I didn't know how they'd react. Well, I walk into my house for a few mintues, and when I come back, the box turtle (later named Dr. Fussion) is on top of my turtle, (Stockholm) and is clawing at his limbs. I pulled him right off.
I gave Dr. Fussion some food, gave him a good cleaning and some water, and sent him on his way. I didn't really have what it takes to take care of another turtle, so I had to let him go.
So, if anyone knows if this was a bad idea (I'm new at turtle owning), or if it's just some natural thing, let me know.