The Magic Potion would be made from a hlaf-empty yoghurt pot, plus added ingredients such as barbeque crisps, bread crusts, apple pips and anything else to hand. The challenge was to make it as big and filthy a mix as possible, and for it to be stirred clockwise with the dinner-lady's pen, otherwise it wouldn't work.
The hapless yogurt owner would then have to eat this mess. If sucessful and was able to keep the mix down for more than ten minutes they were crowned "the Great Sage" for the lunchtime. If they lost the contents of lunch within the ten minutes, they were made to eat grass, because that's what cats do when they have a dodgy stomach.

After George's Marvellous Medicine was read on Jackanory (by Rik Mayall), my sister and I elected to make our own version. But rather than having curative properties, ours would be deadly toxic, and we would use it to poison the children at our school for whom we harboured a dark hatred.
So a Stork Margarine container was procured and a series of top-secret raids on household cupboards was organised. We managed to include a paracetamol, numerous cleaning products, goldfish medicine, Jolen facial hair bleach and shampoo. In a fit of conscience, my sister threw the medicine down the lav while I was occupied, riding around the garden in horse form. Her feeble excuse was that “we can’t just go round poisoning people at the school”. Surely she had not thought this was any more than a childish game? I wasn’t really going to poison anyone; I just wanted to make sure they didn’t go down with fin rot.