In the 1990's, Pepsi released four different new can designs called Cool Cans.  At first, they look innocent until you stacked two cans of the same design on top of each other revealing the word "SEX".

"Sex" is a word that triggers an unconscious response in humans.  Other words that trigger a response are "kill" and "death".  Some advertisers insert skulls or images of dead celebrities into ads to illicit the same response.