Why do they call a police informer a grass?

Question

I know the answer to this one so its ten points for accurate answer.

HEY!!! IVE TURNED YAHOO ANSWERS INTO A QUIZ!!

Answer 1

Snake in the grass?

The grass has greener information than the cops have??....might be time I gave up.  I like Aces High answer

Answer 2

It comes from 'Whispering grass'.The wind passing through the grass,carries secrets.

Answer 3

Easy bruv, grass in the park i.e nark

Answer 4

grass basically means to tell of someone to get them in trouble and if someone informs the police they are known as a grass.

Answer 5

because they do :)

Answer 6

because he's the basis of the operation?

Answer 7

Because the grass whispers to the trees, and the trees tell the breeze, then everyone will know, cos you told the blabbering grass.

Answer 8

It appears to derive fom 'grasshopper'.That is a reference to someone who 'shops' someone to the local police.  In the 17th century 'shop' was another name for prison.

But I imagine another reason for its popular usage is the way it rhymes with a certain part of the anatomy - and splitting things on those you know is still frowned upon.