Hopefully your Fourth of July holiday did not prominently feature vomiting—mine did. Long story short, my "friend" accidentally ate some chicken salad that had been kicking around for a month. This led to his being convinced that he needed to puke it up right away, before any potential food poisoning could set in. Fingers down the throat proved insufficient, so it was off to the pharmacy for Ipecac... FUN FACT! You can no longer purchase Ipecac at the pharmacy—they pulled it from shelves because too many people were using it for gags... pun intended.
Anyway, the solution that ended up working involved fish sauce, the business end of a toothbrush, and so much heaving that he ruptured all the capillaries in his eyelids (seriously), but while things were still in panic mode, I tried to help by googling "inducing vomiting" on my phone. Of course, there's a wikiHow on the subject, which provides some semi-helpful suggestions. One of them is Ipecac, for instance, and a mustard solution about which they say "there is little scientific evidence to suggest that this is effective and safe," and my favorite, watching someone else vomit (step two of this method: "Ask someone to vomit." Which kind of brings the whole thing back to square one, don't it?).
But it's the illustrations that really make it:
The whole thing's worth a read.