Now that sounds exciting. I've only had animals sneak on stage while doing outdoor theatre. For a production of Streetcar we had a bat land onstage right at the top of Act II, very close to our Stella, who was deathly afraid of bats, giving us a few extra lines of "Stanley, there's a bat in the bedroom, get rid of it!" At another performance we had a raccoon sneak along the extreme side of house left (nobody was seated in that section during a sparsely attended, and very hot, Tuesday night) and crawl right under the bed during Blanche's "I want magic" scene with Mitch. I don't know what happened to it. Luckily it snuck out before Stanley came back for the big scene between him and Blanche, because I was ready to stop the show before that if it was still under there for that scene (I didn't want to find out what a raccoon would do when people were suddenly getting thrown down on top of the bed it was hiding under).