Steve enters the Principal's office twice, and each time the door is hinged on a different side.
The man whose brain was switched with Klaus's is shown at the 1986 Winter Olympics. There was no Winter Olympics in 1986; Winter Olympics were held in the same years as Summer Olympics (for example, 1984 in Sarajevo, and Calgary 1988: XV Olympic Winter Games (1988) until 1994)
When Roger enters the basement to find the Jack-in-the-box Man tied up, they are both startled and shout. However, the Jack-in-the-box Man emits Roger's voice and Roger emits the Jack-in-the-box Man's voice.