In-jokes in Movies

The Birds (1963)

Near the beginning of The Birds, when Tippi Hedren is walking down the street (having just passed the San Francisco poster), she turns to acknowledge a wolf-whistle from a passing boy. This is an in-joke.

Hitchcock had first seen Hedren in a commercial for Sego diet drink made by Pet Milk. There was a shot in that commercial where she turns and smiles in response to a wolf whistle, and Hitchcock decided to reference it here.