Can someone please explain this to me? I come from an undeveloped country.

Scrijjy Doo

In the UK teachers who replace absent teachers are called supply teachers. Author is playing with supply/supple.

Vivvy En

Thanks, Vivvy. I had no idea either. We call them substitute teachers in NZ. I thought it was just a really stretched pun 😉

James Lennox

Thanks, Vivvy.

Scrijjy Doo