Here are some examples:
* "The angry dog gnashed its teeth at the mailman."
* "The patient gnashed his teeth in pain as the dentist worked."
The word "gnash" can also be used figuratively to describe something being ground or crushed into pieces. For example:
* "The waves gnashed the rocks on the shore."
So, "gnashed" describes the action of grinding teeth, often in a forceful and aggressive way.