...in which Alison reveals how she got her Brownies Biohazard badge. Kids, if you try these experiments at home, don't let your parents sue us. People who enjoy this sort of thing are recommended to read How to Play with Your Food, by Penn & Teller, which contains lots more fun things to do (though not, I think, any of these).

Lava Lump: Thanks to Pam Wells and (indirectly) Moshe Feder for this one. Take a bar of plain soap, and microwave it on High for a couple of minutes.

Trebor Luminescence: Take a packet of Polos^TM into the cupboard under the stairs, along with a friend. Shut the door so it's nice and dark. Break in two. The Polo^TM, not the friend.

Etna: Bit traditional, this one. Mix vinegar and baking soda. Not entirely successful for the Confab committee; probably on account of only being able to find balsamic vinegar.

Rocketry for Beginners: Next time you're having people round for dinner and serving Italian food, get some of those nice Amaretti biscuits to have with the coffee. The ones you need have the biscuits individually wrapped up in printed tissue paper. Eat the biscuits. Form the paper into a cylinder so that it will stand up on end on a plate. Using a match, light the top of the cylinder and allow to burn until it goes out. Remember to catch the ashes. Also fun in Italian restaurants, but you might wish to leave a bigger tip.

Flour Power: Thanks to Mike Scott for this one; none of us have dared try it. Take a large empty tin, of the sort used for drinking chocolate. Go outside. Spread some flour on the base. Add a nightlight. Light the nightlight. Put the lid on the tin. Retreat to a safe distance! Throw a rock or some similar at the tin in order to jiggle the flour.

Poor Man's Minefield: Try the following, mix ammonia, iodine and sugar. Paint the resulting liquid in a thin layer onto a flat surface (such as a floor) and allow to dry. Anything that touches the surface goes bang. Be very careful disposing of any solid residue, we're talking serious contact explosive here.