Very cool thing I learned in high school-
There is a well known experiment called the Asch conformity experiment in which subjects are placed in a room with several other people (all planted by the researcher) and all are asked which of several lines displayed is longest. When all of the confederates would pick a line that was clearly not longest, even when the person was sure the correct answer was different he would still pick the one chosen by the other in the room.
How did Solomon Asch conceive of this experiment? Back when little Shloime Asch was a seven year old boy in Poland he stayed up until the end of his first Seder and was told by his grandmother to watch the kos of Eliyahu because he was going to come and drink from it. He kept watching it and watching it until he was convinced that the cup was emptier because he was told it would be. After he grew up and became a well known social psychologist, he became intrigued by what has caused this feeling in him and created the conformity experiment.
My grandmother actually used to do that sometimes but she would jiggle the table first- maybe when I grow up that will be the next experiment.
/endnerdrant