Experts out to understand the different messages hidden in a yawn say that it could also reveal a desire for sex.
Academics from Europe, the U.S., India and the Middle East attended the first ever International Conference on Yawning and discussed topics that ranged from "Yawning over a Life Span" to "Yawning in Non-Human Primates" to "The Theory of the Hidden Sexuality of the Yawn."
Ditching the old theory that we yawn because of lack of oxygen, they agreed that a range of emotional triggers probably sets off the yawn response. Interest, stress and even sexual desire may play a factor.
"We can send a man to the moon but we cannot explain this most trivial of acts," ABC News quoted Dutch academic and author Wolter Seuntjens as telling Britain's Daily Telegraph newspaper.
It's his theory that some forms of yawning send out an erotic subliminal message.