The well-known known illusion above can be seen in two ways: as both a duck and a rabbit. Which do you see first ? and if you see one, can you also see the other ?
Err, don't people yawn because they're bored and/or tired ?
Yes, it's true people do yawn more at bedtime or after they've woken up and they do yawn when they're bored (people even yawn in their sleep).