“She was a stray that I took in.”
A coworker is visiting your house for the first time. You have a cat which doesn't like strangers very much. The coworker comments on the cat's personality, so you explain why the cat is shy around people.
She was a stray that I took in.
The phrase "take in ___" means to let a homeless animal live with you.
If you use words like "it" or "them" as the object, they will come between "take" and "in":
They wanted to take it in. I was like, "No way."
Sometimes people also use the phrase "take in ___" to talk about letting a person live in your home.
A "stray" is a pet which doesn't seem to have a home or master. Cats and dogs are most often called "strays".
You can call an animal "a stray" or you can say "a stray cat", "a stray dog", etc.