Mensa is an international organization whose members have an IQ of 140 or higher.
A few years ago, there was a Mensa convention in San Francisco and, during the break between the morning and afternoon meetings, several members lunched at a local cafe.
While dining, they discovered that their saltshaker contained pepper and their pepper shaker was full of salt. For these "brainiacs" this became an intriguing problem, how could they swap the contents of the bottles without spilling, and using only the implements at hand?
Clearly this was a job for Mensa! The group debated and presented ideas, and finally came up with a brilliant solution involving a napkin, a straw, and an empty saucer. Before attempting to implement their solution, they called the waitress over to dazzle her with their erudition.
"Ma'am," one of them began, "we couldn't help but notice that the pepper shaker contains salt and the salt shaker..."
"Oh," the waitress interrupted. "Sorry about that." She unscrewed the caps of both bottles and switched them!!