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'.
(..) No, we're all waiting for the doctor. It's the stud farm. - Everyone walked out of languages. - Let's go to the X-ray... There's no X-ray today. The doctor's boiling jelly. And what if he took my graceful companion with him, beautiful Bacilisu? Who here has an invitation to go to Africa? (..)1989 Dva lidi v zoo