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In The Addams Family, the children brew "lemonade" which, when given to Lurch, causes him to breathe a fireball. And since this is Lurch we're talking about, he probably got off light compared to what it would do to a normal human.
Aladdin: Jasmine accidentally causes a street performer to swallow a torch, immediately after which he belches out fire.
In the first Critters one of them swallows a fire cracker; it burps up a flame after it explodes inside of it and it dies.
Played straight in Dumb and Dumber, when Harry and Lloyd laced their traveling companion's diner burger with "atomic" peppers. The result was so intense that it nearly killed him by making his stomach ulcer flare up. Then Harry fed him rat poison - thinking it was his ulcer medication - and actually killed him.
A subplot of A Fine Mess is that Dennis Powell (Howie Mandel) wants to open his own Indian food restaurant that would specialize in curry, although he's never actually tried it before. Dennis's first experience eating curry at a restaurant with Ellen has him downing drinks, eating leaves out of the flowers on the table, running to other customers' tables to drink whatever they have until he finally just starts SCREAMING!