This occurs when, during a normal
fart in the standing position, a
small grape-sized poop is rapidly ejected from the anal passage. This "
secret grape" is undetectable, until one sits down, at which point, the grape is no longer secret.
John and
Keith are walking down the road, Keith lets rip, the two
friends chuckle. Later, they come to a bench, the two
friends sit. Keith's face turns red and an ominous odour fills John's nostrils. The secret grape is no longer secret.
John - What's that smell Keith? and why's your face so red?
Keith - *stands up, squashed grape falls from trouser leg*