Daniel Stern ("Marv") agreed to have a tarantula put on his face for the movie. They took safety precautions out of concern that the tarantula would have been scared into biting him if he actually screamed. To prevent this, they filmed the scene with Daniel just mouthing and miming a scream, but without making a sound. The sound was added later in post-production.
Here are some more fun facts about the movie:
• In the scene where Harry attempts to bite off Kevin's finger, Joe Pesci actually bit Macaulay Culkin, leaving a scar on his finger.
• The role for Harry was offered to Robert De Niro but he denied it. Can you imagine Robert De Niro in Home Alone?
• Daniel Stern accidentally said the "s-word". You can hear it when he is retrieving his boot through the doggy door at 55:27 on the DVD.
• The famous pose on the movie poster where Culkin has his hands on his face while screaming is a reference to the famous painting "The Scream" by Edvard Munch. For more cool facts click the Source!