system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel] Is the Hulk transformation painful?

It looks like it, i mean his skeleton and well everything is expanding dramatically at an outstanding rate! And turning back is just has painful, on a side note what happens to all that extra mass such as cells come from/go?
gpt
I think I've read that the added mass comes from another dimension, or the energy to create that mass does or something. There's lots of tapping into other dimensions in Marvel (Cyclops's eyebeams, Nightcrawler's teleports, etc.)

I would imagine that it is very painful, but when you're fueled by rage that's probably helpful. Changing back must be less traumatic, or the process would probably just kick off another Hulk out.