Guess What It Is

You probably have a few of these in your house, but I bet you never saw them in quite the way Valerie Worth does:

Closed, it sleeps
On its side
Quietly,
The silver
Image
of some
Small fish

Opened, it snaps
Its tail out
Like a thin
Shrimp, and looks
At the sharp
Point with a 
Surprised eye.

Post a comment with your guess, I'll reveal what the item is tomorrow!