For all slipperings you were told to “bend over” or “touch your toes” and you always complied, just hoping it would be only three whacks (was never less than three) and not, say, six.
And it always stung!
I was often on the receiving end of a slippering for the most trivial of reasons.
Our sports / p.e. teacher was lethal with a strap, which he used frequently. Sometimes, he didn’t have the strap to hand so would use a slipper – and he knew how to make it sting! I saw him give the strap / slipper to boys on their underpants or swimming trunks, and was in this position myself at times.