I'm watching "The Grudge" and, of course, there is a scene where one of the characters sees a red liquid on the floor, and proceeds to stoop down, put his fingers in it, and look at it with a puzzled look on his face. Who would do that? And yet we see it time and time again. If you ever saw a movie called "The Boogens", there is a scene where a girl goes to a friend's house, walks into the kitchen, sees a pool of blood (her friend's) on the floor with a smear leading to the basement door. And, as mandatory for a horror flick, she puts her fingers in the pool of blood, follows the smear to the basement door, goes down the basement stairs, and is killed by "the boogens".
If you ever come to my house and see a pool of blood on my kitchen floor with a smear leading to my utility room---DO NOT--I repeat--DO NOT put your fingers in the blood and definitely DO NOT follow that smear. GET OUT of my house and call the cops. Let them go in with their guns drawn.
http://www.pitofhorror.com/features/boogens.html Do the writers of horror films really think we're that stupid?