The verb ngon describes what water does when it's boiling: It's bubbling. Also, if you blow with a straw into a glass of water, then it's also bubbling, i.e. making bubbles. The person does not ngon, they ngonmoH the water.

The noun is ba'Suq "bubble".

SEE ALSO:
pub      boil (v)
jo'      blow into a container of some kind, inflate (v)