Mensa, as you probably know, is a national organization for people who have an IQ of 140 or higher.

Several of the Mensa members went out for lunch at a local café. 
When they sat down, 1 of them discovered that the salt shaker contained pepper & the pepper shaker was full of salt.

How could they swap the contents of the 2 bottles without spilling any & using only the implements at hand? 
Clearly this was a job for Mensa minds. 

The group debated the problem, presented ideas & finally came up with a brilliant solution involving a napkin, a straw & an empty saucer. They called the waitress over, ready to dazzle her with their solution.

“Miss”, they said,” We couldn’t help but notice that the pepper shaker contains salt & the salt shaker – ” but before they could finish, the waitress interrupted, 
“Oh! sorry about that”.  She leaned over the table, unscrewed the caps of both bottles & switched them. 

There was dead silence at the Mensa table.