As head, I did use a slipper. I used it when I felt the offense did not deserve a caning but deserved something stronger than a lecture or detention/lines. I did have a proper slipper, with the top cut off, a size 9. By a proper slipper, I mean one that started life as a house shoe. Mine dated back to about 1930 and in those days they had a fairly thick, but flexible leather sole. In most cases two whacks with this across a boy’s pants was enough, to provide a short sharp sting. It was very rare for me to slipper a boy on his bare bottom.