After Morris consumes the fruit punch with alcohol in it, a couple minutes later we see him walking down the street with a cigarette in his mouth. The dean of the school is driving along, and Morris pukes on the wind shield, releasing the cigarette from his mouth. The very next clip we see him with the cigarette in his mouth again, then the next clip it's gone.
When the frat boys are sniping people with paintball guns, their paintball guns do not have hoppers, which hold the paintballs. While paintball guns can still hold up to 3 shots in the load chamber without a hoppper, they are unable to fire multiple shots in semi-auto as portrayed in the movie without reloading or using a hopper.
When Kevin (Drake Bell) receives a message on his cellphone at the beginning of the movie, the alert reads "New Text Message", but when Kevin opens the cellphone a Video Message plays from his friend Carter (Andrew Caldwell).