I'm under the impression that chams can actually "unstick" their tongue. There have been multiple occasions when a roach or worm has made it's way to my finger before the cham starts to go for it... then when they do shoot, you can feel the almost sandpaper/tentacle feel of a cham tongue. Recently, my female did this and started to pull my finger towards her mouth, and pull herself towards my hand. When she realized this she "let go" and still got the silkie.
So long as the object they hit can't damage them... it's just part of owning a cham. As a side note... never feed from pointed tweezers and such as that can and will substantially damage the tongue. [Not saying you do... just putting it out there]
Best wishes!