I like it when my pleco bites my hand. It's his way of saying
GET THE *&%* AWAY FROM ME YOU STEWPID EEDIOT!
I hold mine mostly open palm or across the fingers. I have seen and heard too often of people not knowing how to hold plecs holding the head, thumb and forefinger, and the plec thrashes and goes flying or worse the person reacts and tries to hold tighter.