As Baxter is sitting on the roof and drinking beer, Luke, who is on the ladder, calls out to him and Baxter drops the beer. It disappears before right before the edge of the shingles.
After Christy's second injury while she is trying to carry soup at the restaurant, she goes out the in door of the kitchen. Anyone who has worked for even one day in a restaurant would not use the door to left whether they are coming from customers side or the kitchen side. This unwritten rule has been used for long to avoid collisions while using swinging doors. Breaking the rule has been a formula for humor in three stooges films and many other comedies for a very long time.
Christy injures her ankle but walks around with her knee stiffened. This movement uses the muscles in a non-natural way and is likely to lead to further injury.