These start off as small plastic like bb's. You place them in water and they slowly absorb water. They can then become this size, so they're like >95% water. I asked my teacher what would happen if someone ate one.
They'd get lodged in your stomach and intestines, absorb water, and cut off your GI tract and kill you.
Rainbow medley w/ prime eligibility
TL:DR Don't eat these
edit:added links