In plenty of packages that need to stay good and dry you'll find little packages that say "do not eat". This is why you should definitely follow that advice.
Inside those packs typically lurks silica gel, which sucks up moisture by adsorption, in which water adheres to the surface of the material. In fact, a single grain can suck up 40 per cent of its own weight in H20.
And that's why you shouldn't eat it: while it won't kill you, it will suck up pretty much all of the moisture in your mouth and — if you get that far — throat. Which, SciShow claims, would make the Cinnamon Challenge look like a walk in the park. Gulp. [SciShow]