Hello, Professor McGonagall,” said Moody calmly, bouncing the ferret still higher.
“What — what are you doing?” said Professor McGonagall, her eyes following the bouncing ferret’s progress through the air.
“Teaching,” said Moody.
“Teach — Moody, is that a student?” shrieked Professor McGonagall, the books spilling out of her arms.
“Yep,” said Moody.
“Moody, we never use Transfiguration as a punishment!” said Professor McGonagall weakly.

Author: J.K. Rowling