Stress in humans can affect how optimistic dogs feel, research suggests

Study got dog owners to either take a maths test or do something relaxing and observed effect on pets' emotions

The ability of dogs to sniff out stress levels in humans has been known for some time.

But the relationship between woman and man's four-legged best friend is two-way, and scientists now believe they have discovered that when a dog senses a person in distress, it has a knock-on effect in the behaviour of the animal - most notably, it makes them pessimistic.