For what it's worth, irl I spend part of my free time designing and building props for no real reason whatsoever (cosplay stuff, reworked nerf guns, etc). I also like to engineer ways to do out of the ordinary things just as a hobby.
When playing around with belly inflation ideas, I always found the most common go-to's...balloons or beachballs under clothing...oddly unrealistic and unsatisfying. But a thought came to mind and I'm trying to construct/test a workable model to make a more realistic/enjoyable belly inflation device (kind of like the red belt I came up with designed to pop at the buckle once it was under a certain amount of strain).
Likely this has already been done but my idea to test is this...using a very large balloon (likely 36"...I tried smaller but none of them seem to be big enough), cut the neck off and stretch the balloon across a flat surface like a drum. For the initial test I am using a cheap plastic plate. The plate already has a small hole cut/melted into it with a length of aquarium tubing fed through and sealed with glue. A small scale preliminary attempt also says I have to find a way to firmly secure the back side of the balloon. Theory goes, if I start pumping air into this set-up, the disk should go from being relatively flat and will start to bow outward like an expanding belly. Overly simplistic design and like I said, I'm sure it's been done before.
Was curious about opinions or if anyone has come across this concept before.