VELCRO .. we had a similar situation. we are not sure how it happened...basement window broke, we put a piece of plywood against it, the plywood had been pushed away from the window, and we found a cat in a doll cradle (not being used). Thing is... it's our neighbors cat. We have 4 dogs. Guess he was looking for a warm place to sleep. We tried several things to block the window. he keeps finding a way to get in. I think its humorous.