I brought this behavior up to my friend who had a turtle for a while, and she said hers did the same thing! She later informed me that it is actually part of a mating ritual. While I love Pluto, and am devoted to him, I am not about to get another turtle. But I do from time to time put a triceratops finger puppet up to him, and now, two little relax bears I got from the awesome JapanLA shop.
It may be a love-hate relationship, but at least I am keeping him stimulated. Plus it is pretty cute.