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Waiters use nodding trick to boost restaurant tabs

A tip to trick people from the Wikipedia:

A Sullivan nod is executed by nodding slightly, by approximately 10–15 degrees, when the item it is hoped the customer will choose is reached. The key is to make the nod perceptible, yet subtle, so as to not distract. The nod is best done with lists less than 5 items in length. Studies have concluded that 60–70% of the time, a Sullivan nod will result in the customer choosing the ‘recommended’ item.

Found: here.