What's a plugged nickel?

In the column about hanging bags of water to repel houseflies, it say that some insects’ eyesight is not worth a plugged nickel. I’ve heard it many times. . .but what is it?


to “plug” is to remove a coin’s center. 'round these parts, it’s common for a coin to be plugged by, say, a .22…in earlier times, the center of a coin was often made of gold or some other precious metal. dishonest folks would take out the center and replace it with something less valuable.

[pirate voice]I says we plug ‘im, an’ see if 'e’s ripe![/pirate voice]