Human
Prove you are human: How many dots are on the board?
One… uh… four… AAAAAH! AAAAAAAAAH!
Welcome! Thank you for screaming.
(This is based on an illusion discovered by Jacques Ninio)
It’s Facebook! I was going to be screaming anyway!
If your reaction is 'but it's easy to count the dots' you might want to check your motherboard.