The Bayfield University Baby killer costume was designed by Tony Gardner, who also designed the Ghostface mask, the horror icon of the Scream franchise and which is a reworked version of the Father's Death Halloween costume.
The theatrical trailer utilizes the song "In Da Club" by 50 Cent as Tree's birthday ringtone. However, the final film does not feature this as the crew and studio could not acquire the rights. As a result, an original ringtone composition was concocted.
The scene where Tree walks through the campus quad naked had to be done quickly; given that it was being filmed on an active college campus, this presented the risk of students witnessing the scene being filmed and/or taking photos. The crew took extreme precautions to clear away any potential onlookers. In the end, they managed to do just 2-3 takes.
The original script written by Scott Lobdell included material intending to make the film R-rated. Some scenes involved grislier death depictions that were entirely altered by the film's director Christopher Landon.
The scenes where Tree leaves Carter's dorm room and walks through the campus quad, with the same specific events happening each time (i.e. The couple getting soaked by the sprinklers, the car alarm going off, etc.) took two days to shoot. At one point, the sprinklers malfunctioned and couldn't be turned off, costing the crew at least an hour of filming until they were finally able to fix it.
When asked why a baby mask: Christopher Landon says he needed a combination of something that would pass for a mascot on a college campus, that was both scary and funny at the same time, plus he was expecting a son at that time, so he had "baby on the brain."
The trivia items below may give away important plot points.
An original ending featured Tree Gelbman murdered again, thus entering another time loop. The test audience reacted furiously to this ending, feeling betrayed that the protagonist, after becoming a better person, could not break free. This ending was conceived as a way of leading the viewer to believe it was never going to end.
When asked the cause of the time loop, Christopher Landon says there is a definite reason for it; and if the viewers look closely at the film, there are easter eggs pointing to the cause - and one is really big.
When Tree and Carter are sitting across from each other and Tree eats the cupcake, the shot mirrors the final scene of Sixteen Candles (1984), with the boy and girl sitting cross-legged across from each other in front of a window with the candle(s) on the (cup)cake burning in between them.
Carter points out the similarities between Tree's situation and the film Groundhog Day (1993). There are in fact a few scenes that directly parallel that film's events. Just like Phil, Tree proves that she has lived through this day by correctly pointing out several events about to take place around her. One of them is a frat brother passing out, whom she helps with a pillow. This parallels a scene in GD where a kid falls out of a tree, which Phil memorized and catches in one of his errands. Phil points out that a waiter in the diner is gay, and Tree eventually finds out that Tim is gay. Her repeated unwanted encounters with Tim are similar to Phil running into Ned Ryerson. Two of Tree's deaths involve getting hit by a bus and hanging herself in a bell-tower. Two of Phil's suicides involved walking in front of a bus and throwing himself from a bell tower. Lori's last name is also Spengler, which was the name of GD director Harold Ramis' character in Ghostbusters (1984), which also paired him with Bill Murray.
In the scene where Tree is locked in the cop car, and the masked killer ignites the gasoline trail, the perception is that it is lit with the birthday candle that was on her cupcake. However, the candle on the cupcake was red. The candle that lights the gas is blue.
During the climactic fight, Tree punches Lori in the throat and forces the cupcake into her mouth. A blow like that to the throat would cause the esophagus and windpipe to swell shut, rendering Lori unable to breathe or swallow the cupcake.