what does it mean when they hold their mouths open? he is not hissing or puffing up. i was trying to hand feed him a super worm and he just started opening his mouth, no tongue action or anything....hes continuing to do it even after i stopped trying to feed him.
If he was sitting in his basking spot, then it may be a bit too warm. Chameleons will gape their mouth open to release heat when they get too hot. Try a lower watt bulb or raising the fixture a few inches.
If he has a foamy saliva, audible breathing, or any other troublesome symptoms, he may have a upper respiratory infection, which will need immediate vet attention. At his age though, I am betting he is too warm. A baby veiled's basking spot should be around 80-85.