QI, the BBC show about comedians coming to grips with trivia that's even funnier than they are, has added a regular science installment. This means we get to watch everyone's favorite Harry Potter audiobook narrator make a bargain-basement lava lamp.

Three parts vegetable oil, one part water, a little food coloring, some alka-seltzer and an empty tennis ball tube is all it takes to make yourself a cheap lava lamp. Getting four comedians to come over and intentionally try to screw it all up will probably cost you a little more. Also they will heckle you while you tell them what to do.

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Stephen Fry is always entertaining but my favorite part of the piece is David Mitchell, who says exactly what I was thinking from the moment Fry puts a lid on the top of the tube, trapping the gases inside: "Won't it explode now?"

According to an outline of the experiment, yes, it most certainly will explode if too much alka-seltzer liberates too much gas, and if the lid is sealed. It should at least blow the lid off. That doesn't happen on camera — but fortunately we have another disaster to entertain us at the end.