There was an excellent question on Twitter that caught my attention:
I think firstly this is not quite a science question. If you need reliable answers to questions about fictional things then mathematics is the place to turn…
But first a diversion into biology. The space that forms your alimentary canal isn’t really you. It is really a great big hole that goes through you. The stuff that goes in there gets mashed and melted and broken down but it is only as that stuff crosses over the membranes that separate you from your innards that the stuff becomes part of you. The stuff in your gut is no more you than the stuff on your skin or in your hair. The stuff in your stomach (etc.) is not you. Therefore, the stuff in Bruce Banner’s tummy (or the Hulk’s) isn’t Bruce Banner. Hold that thought.
Topology is a lovely branch of mathematics. It is a way of looking at spaces without getting too hung up about shape. For example we can stop thinking about how Bruce Banner looks different to The Hulk for a moment and instead consider them both more simply.
Bannerhulk-space is the space occupied by Bruce Banner, The Hulk or intermediary states between the two. When Bruce is Bruce, Bannerhulk-space is small. When the Hulk is the Hulk, Bannerhulk-space is at its largest. Make sense? OK, now flip that. What about Not-Bannerhulk-space? That is all the space in the universe that isn’t Bannerhulk space.
Now when Bruce is Bruce, Not-Bannerhulk space is at its largest. When the Hulk is the The Hulk, Not-Bannerhulk space is at its SMALLEST. Aha! Now what about The Hulk’s guts? That’s part of NOT-Bannerhulk space! That doesn’t prove anything but it does point to the fact that we should assume (as a starting point) that The Hulk’s guts are actually SMALLER than Bruce Banners.
Hmmm. Can I show this? I can! Topology again. A person is nearly, topologically, a torus i.e. a doughnut shape. People aren’t quite a torus because of our nose holes but we can ignore those (no, your genitals/urinary tract don’t count as holes topologically – sorry).
We can model the Bruce Banner-Hulk transition as a torus with changing radii. There are two to consider – the radius of the ring overall and the radius of the tube that forms the torus. Now if The Hulk was simply a scaled up version of Bruce Banner then there wouldn’t be an issue – and also the special effects in The Avengers would be much simpler (paint Mark Ruffalo green and have him stand closer to the camera). Instead The Hulk gets bulkier as well as bigger – the equivalent of both radii increasing but the radii of the tube increasing disproportionately.
Let’s see what happens:
Now maybe you are thinking at this point that all of the earlier part of this essay was really just a rationalisation for the time I spent making that GIF…in which case…yeah, maybe.
Back to biology. When Bruce Banner turns into The Hulk, I think the mathematics shows that his alimentary canal will actual constrict. This will force the contents of Bruce Banner’s digestive system out through his orifices – possibly violently so. Now, I note this doesn’t happen in the comic books or movies but maybe it occurs off screen. Just saying.