I've Created a Monster

Pearl likes to gnaw/suck on my hand. A lot. Anytime my hand is near her mouth she lunges for it. We play this game I call Back Up, Back Down, where I lounge on the couch and lay her sort of perpendicular to me, and she holds onto my thumbs, and whenever she crunches her abs and lifts her head I pull her into a sitting position for a little while, then back to laying down, saying "Back up!" and "Back down!" at the appropriate time. She loves this game, and I suspect it is because when she is sitting up she has the opportunity to chomp on my hands. However she only likes to chomp on my hand while we're playing this if she is holding on to both of my thumbs. Holding on to only one thumb is unacceptable and leads to wailing. Why, I don't know. She's a weirdo.