Our two girls' very favorite book these days is Good Night, Gorilla. It's a charming picture story about the gorilla freeing the other animals from the cages and all of them ending up in the zookeeper's bedroom, and having to be put back to bed in their cages by Mrs. Zookeeper.
Usually when we read books like this we make ASL signs for the animals, but this has several animals that we haven't found the signs for, like armadillo and hyena and so forth.
But today I realized that Catherine already had her own sign for gorilla. She was making the sign for GIRL for the gorilla.