Chubbyemu did a video awhile back about a guy who blocked his intestines by overdoing it on fiber supplements - he was mixing so much powder into his drinks that it formed an indigestible lump that had to be surgically extracted.
I’m thinking something like that.
I actually had a vaguely-close experience where I took fiber supplements (psyllium-type stuff) but forgot to drink enough water. It made my guts feel like cement for half a day and I panicked a bit and started drinking lots of water, but there ended up being no bowel obstruction.
Bowel obstructions are fatal over the course of a few days if not cleared somehow. Lotta different ways for that “someone” to have a bad ride.