drumming on one's belly; having one's fill
Literally 'belly drum'; refers to the act of patting one's full stomach like a drum after eating, or the state of being full. Often used in the phrase 腹鼓を打つ (to drum on one's belly).
I was so full I unconsciously drummed on my belly.
After the meal, he smiled contentedly while drumming on his belly.
Compound of 腹 (belly) and 鼓 (drum), referring to the resemblance of a full belly to a drum.