I’ve seen various mock-up photographs and clips and it’s clear that none of them have ever seen a real slippering, they hold the thing in the middle and sort of shove it at the recipient, but our PE teacher held it by the end of the heel thus allowing the flexible rubber to slap into your bottom with a real crack. He also made you touch your toes, whereas the Headmaster just had you bend over with your hands on your knees.