When Heather gets out of bed, she puts her slippers on and walks over to her vanity mirror. Later when the spider falls to the floor and she crushes it, she is barefoot.
During the slow song in the homecoming scene, the people in the background seem to be dancing to a fast song, and then back to a slow song, in several quick cuts.
When the twins are at the library computer, they are seen reading an article about a woman's suicide and quickly turn off the computer when the coach enters. When he turns the computer back on, the screen doesn't match the article that they were reading when they turned it off.
When Sam is on her bedroom floor, her striped/small floral comforter is on the bed behind her. Then it changes to a yellow-and white-pattern with large flowers after only a few minutes.
The article on the library computer is about a 1982 suicide. It's established by the character reading the article and by two current-event indicators in the article itself that the article was written the same day as the 1982 suicide, but another part of the article inconsistently refers to the original 1969 kidnapping incident which led to the suicide as happening 35 years ago. 35 years after 1969 would be 2004, the year the movie was filmed--not 1982, the year of the article.
When Samantha hands her twin the paper to show him the article about the boys, you can see the story about Mary Banner that is shown later in the movie.
The male lead is seen reading a newspaper article; the headline says "Serial Killer Arrested at Pendleton University" but when he reads the headline aloud, he mentions the professor that killed students at Alpine University, which doesn't match the headline from the paper he's reading.
When David goes to tell the boys that he knows what they did, Buck's microphone is visible in the back of his pants.