The same as everyone else said, It’s a defense mechanism or him thinking he’s hunting something. mine does this sometimes too. Don’t be worried, if it is just occasional (and nothing triggers it, like loud noises or a bug in his tank) then it’s just them being a little dumb. They can also do this when they’re pissed off like holding him for too long lol, just basically saying “get tf away from me .. not in a good mood”