When we lived in Chicago a possum got stuck in our window well once. It was sound asleep. While we figured out how to get it out of the window well (it was too deep for it to climb out) I went to the basement and turned on the light. That awoke the possum who then lunged at the window. I was very grateful for the glass as it was rather terrifying looking when startled!

We put a board down in the window well and Possum was able to climb out.