A random man (Jayden Curtis, a set decorator) walks into the shot, trips over, and hurriedly runs out of shot in a panic. This was so funny that the actors ad-libbed him into the scene, and the directors loved it so much that they wrote him into the script again as a side character.
A Boom mic was briefly visible, but the directors loved the shot so much they decided to keep it, and edited out the mic in post.