Didn't your mom ever tell you not to bite people!? You shouldn't bite and explode them either. It's not nice. Although when Natsu actually chomps down on the 'clawed hand, with that look in his eyes, the demon smirks almost triumphantly, ready to boast and brag that biting him has no effect when ...something about Natsu's expression has a moment of 'wait what?' run through his head.