Can't really trust dogs and cats.
Last time I left my dog alone at home, after driving away I had to return because I forgot something. Usually she's right by the door, yapping and going crazy that I'm arriving back home. This time there was silence. Couldn't find her anywhere. Finally I found her in the stairs, trying to get back down from upstairs, unnoticed. She's forbidden to go there . . . clearly first thing she did, though, as soon as I left and she thought I wouldn't be back for a while.