There are pranks and then there are pranks. Mostly they are devised with evil cunning or innocent fun just to get a reaction out of people or kill boredom.
LG did it to promote their new IPS monitors!
They tested the high-definition screens by installing a 3x3 grid into the floor of an elevator which showed the floor falling away from right beneath ones’ feet! Scary enough to take one’s breath away and not soon forgotten, the people who were the victims of the prank will not soon forget their experience nor LG for giving them hair raising memories for some times to come.