What does Clark hit in the attic in National Lampoon's Christmas Vacation?

In "National Lampoon's Christmas Vacation," Clark Griswold hits a hidden beam in the attic while searching for his Christmas decorations. This incident leads to a humorous moment as he falls and knocks over various items, showcasing the film's signature slapstick comedy. The scene is part of the larger chaos that unfolds as Clark attempts to create the perfect Christmas for his family.