Yawn
Yawning is commonly associated with tiredness, stress, overwork, lack of stimulation and boredom. In humans, yawning is often triggered by others yawning (e.g. seeing a person yawning, talking to someone on the phone who is yawning) and is a typical example of positive feedback. This "infectious" yawning has also been observed in chimpanzees and dogs. Cats both yawn and stretch, though not necessarily at the same time.