Imagine character B of your otp is mouse-sized (or suitably tiny) and has recently been taken in by A, who is doing their best to look after them by providing a home, appropriately sized mini-meals, etc.
One day, A’s parents come over and A tells B to stay hidden because A’s parents don’t about B yet and might not understand. B, not knowing where to hide, finds an open tin nearby and crawls inside, dragging the lid on top leaving just enough open to breathe.
When A’s parents have gone, A walks into the kitchen to hear soft, tinny moaning coming from inside the biscuit tin. They walk over and take the lid off the tin; inside is B, laying against the side and rubbing their swollen belly while reaching out for the next piece of biscuit.
A helps them to soothe their bellyache, they’d eaten one and a half whole biscuits after all, with fingertip tummy rubs. Maybe, once their stomach has settled slightly, A feeds them the last half of biscuit.