That's my best psychotic murderer grin, by the way. (And the start of my Halloween-related posts.)

I'm not completely sure if this plan would work - in fact, I think there are major flaws - but I would think that if you could get enough baking powder into a person, and then get it to expand at once, you'll likely not only have much in the stomach, but potentially some along the pathway to the stomach. So if you get expansion in the pathway, you might block vomit from escaping, and so cause internal bursting.

Unlikely? Yeah. But if it actually worked, you wouldn't stop laughing, either.