Yesterday we were sitting at the dining room table eating lunch. Chii jumped up on the table to go after Sarah's tuna fish.
Sarah: Chii is silly!
Me: Yes, she is *shoos cat away*
Sarah: She and Freya are both silly
Me: Well they are sisters. Actually they are litter mates.
Sarah: What's a litter mate?
Me: Well cats usually have more than one baby at a time - often 3 or 4 - and when they have a group of kittens like that we call it a "litter"
Sarah: Oh! *with sudden clarity* Cat litter!