I think Noah's got it right - it's cause they're drinking a lot at once, and they poop when doing this sometimes.
However, I do not think they are incapable of complex behaviors. I think they are not pure instinct, as some do. I have seen quite a bit of learned behavior over the years. Social interaction is partly learned, for sure, as is their understanding of their surroundings. they learn their cage, and how to navigate. Chameleons don't take a direct path ot an object, they know what the best route is, throught the pathways and branches. I've seen them get back to their roost in the dark. They "know" things, remember them.
I believe this is a major reason chameleons become stressed when moved. It's unfamiliar to them. In nature, this only happens when they hatch - they're never thrown into a new territory. They always move from one to another.
They recognize their keeper - My melleri will climb onto me, without provocation sometimes - but she'll give others a dirty look.
Sure, they do "stupid" things - grabing their own legs, for instance. But they also learn some reall yneat stuff.
My male veiled has some nerve damage in his rear legs. They dont' work well. He sleeps with his back end hanging down, and walks using his front legs more than his rear legs. He's learned to use his tail as a replacement limb. Normal chameleons don't use their tails like he does. He will bring it forwards - sometiems ahead of his rear legs, wrap it around the branch, and brace his back with it. And he does this FAST - as fast as if he was using his rear legs. It took him months to ge tgood at this. At first, he'd just drag his rear legs. Now, he's much better at it.
But then tey do some really stupid instinctive suff - like when th efemale is non-receptive, and I move her out of the way, and he decides that my wrist looks receptive, and he mounts my hand and rubs his vent on my wrist, looking for the cloaca.... an dhe holds on, even after I move him....yeah...pretty gross....
He was like this for a few monutes, looking for my hand's vent.
