He could feel the anger 'boiling up' inside him. [=he could feel himself becoming very angry]
The water in the pot is 'boiling over'. = The pot (of water) is 'boiling over'.
The kettle (of water) is 'boiling'. = The water in the kettle is 'boiling'.
(..) Why read words when you can just kill the stuff the words tell you stuff about? I've read it seven times. There's this water dragon that sprays boiling water at your face. And there's this other one... Yeah. That sounds great. - There was a chance I'd read it... - But now... (..)2010 How to Train Your Dragon