Two key stories:

I was in a workshop on Jewish music, and the teacher tried to get us to clap out a very complex pattern which went with a song about a frog in the kitchen, cooking pancakes for his sister. I never could get the pattern. She said that she had done this song in a nursing home in Israel once, and all the residents tapped out the pattern using their keys. Cute story.

Once I was working in a children's library, and a mother gave her keys to her two-year-old to entertain her. (Why would you give something that valuable to a toddler?) Of course, the kid got bored with them and set them down somewhere.

I will never forget the mother shouting "Abigail, where are the keys?!"

What was the kid supposed to say, "I put them in the 641.5's" ?

The mother finally found them somewhere in the stacks.

So that is a good use for old keys. Make fake key sets for toddlers to play with.