Help! BP have empty belly

[Lolo76]

bp's suck in like that when you pick them up and touch their bellies even my late 09 1020 g fat boy does it. Some say they have tickelish bellies. Totaly normal.

Yeah, I've noticed some of my shy snakes do this... recently I interrupted Mona (big 2000g girl) while she was sleeping, and she sucked in her belly just like that picture. She's a fatty who eats 3 large mice weekly, so I know she isn't underweight! To the OP, have you observed the snake's belly while he's relaxed in the the enclosure?