The MythBusters have already debunked the myth that a few grams of caesium (Cs) or rubidium (Rb) will cause a hand grenade-sized explosion in a toilet. To further test the myth, they increase the amount to 2.5 kilograms and run the test in a bathtub with sodium (Na) and potassium (K).
Professor Anderson leads the group through the underground cave. He almost falls down a deep chasm as he tries to assure the group that he's good with directions. He attempts to use a flare to measure the depth of the chasm, but the magnesium rocks cause it to explode. Hannah then gives him a glowstick, and he uses that to determine that the chasm is about 200 feet deep.