Remus's belly is only tight for the first few seconds. Once Marcellus has repositioned himself, it relaxes, opening up into a much larger chamber that he could actually move around in if he wanted to. In fact, since Remus is so fat, Marcellus doesn't even make a bulge in his belly right now! He licks his beak, then licks his talons, getting the last of Marcellus's flavour off of them. "You're delicious, Marcellus~" he replies happily, beginning to rub at his belly. "Meaty, salty, with just a hint of sweetness~"