Director Howard Hawks used to insist on his actors carrying around duck eggs in their underwear during particularly intense scenes. He believed that the technique would result in more considered, precise performances, but in actual fact they tended to make the actors feel extremely nervous and agitated. Lauren Bacall found the scenes especially stressful, since she had experienced a traumatic incident involving an aggressive mallard as a child.
The director eventually abandoned the practice, instead adopting a technique in which he would remove one item from the luggage of each actor, placing them around the set at arbitrary locations. If the actors accidentally noticed and looked at the items during the scene, they would be forced to read their lines while preparing a cooked breakfast for the entire crew.