cascabel

The very pungent Mexican Cascabel looks a lot like the Cherry pepper when it is growing.[…]In the dry state the skin becomes translucent and the seeds are loose so that they rattle, hence cascabel, which means sleigh or jingle bells. Another cultivar, the elongate Catarina, is often called Cascabel because its dry seeds also make a noise within its translucent dry skin.

The cascabel, instead of being permanently attached to the breech of the piece, is set into it by means of a screw, and thus in reality the bore extends the entire distance of the gun, so that when the cascabel is taken off one can look directly through the gun.