I recognized a peculiar set of words yesterday, and I thought I'd share them with you.

There is a word that paradoxically changes both its number and its gender with the addition of an 's'.
Indeed, it becomes singular where before it had been plural, and feminine instead of masculine.

Maybe it's a well-known puzzle, but I know a lot of them and never came across this before.
I don't know any other words with this property. Do you suppose Richard Lederer does?

Whaddaya think?