Dave's ESL Cafe's Student Discussion Forums

[missdaredevil]

Let's *whip grass*.

What does that mean?

It was said by a talking bug.

[asterix]

There is an American expression, "Let's whup (whip) a s s." It means, let's go out there and beat (an opponent of some sort.)

Because it is used by a bug in your example, the writer has changed the expression to, "let's whip grass!"
It is probably done for humorous effect, especially if the opponents are grasshoppers, and to avoid annoying the parents of the kids who watch the show.