roundworm; intestinal worm
Literal meaning: parasitic worm in the belly. Used in old medical or folk contexts; modern term is 回虫 (かいちゅう).
In the past, herbs were used to expel intestinal worms.
inner feelings; mood-influencing emotions
Figurative use: the 'worm in one's belly' that stirs up anger or discontent. Common in the set phrase 腹の虫が治まらない (cannot contain one's anger).
See also: 腹の虫がおさまらない
I couldn't contain my anger at his rude attitude.
stomach growling; hunger pangs
Figurative use: the 'worm' that makes one's stomach rumble. Often used in the phrase 腹の虫が鳴る (one's stomach growls).
See also: 腹の虫が鳴る
After skipping lunch, my stomach started growling in the afternoon.