She painted his portrait for a lost-cat notice to give all her neighbors. She called his name, she listened for his steps. And in the silence of her missing cat she wrote the song "Man from Mars."
The cat came back, and in an interview of 2000 Mitchell says (among other tales of her four cats),
When I played the song for him, he stood on his hind legs and danced, so he
recognized it somehow. What had happened is that I was outside at night,
calling, trying to hear his voice, and in so doing I heard far into the distance
in my neighborhood. I'd never listened to my neighborhood as closely as I did
when he was gone.
You can hear a snippet of "Man from Mars" from the Amazon.com sampler here. There's another telling of the story at Anecdotage.com.