Eagle eyed guests may have spotted a giant spider, attached to the glass in the Haunted Mansion's Ballroom. The spider and its web were placed to cover a large crack in the glass sheet that helps project the Ballroom's ghastly effects.
The Disneyland Legend is that a kid with a slingshot created the crack, although it could have been a stray bullet from the ghostly duel. Since the giant panes of glass were positioned before the Haunted Mansion's construction was completed, it would have taken a great deal of effort and money to replace the broken glass. Placing a giant spider and web over the crack created a creepy and inexpensive solution to the problem.