A dog expert has invented a device which can tell an animal's mood by measuring the wag of its tail.
A dog which is happy has a wide and horizontal wag
Dr Roger Mugford, who runs the Animal Behaviour Centre in Chertsey, Surrey, claims a dog's wag can show if it is happy, angry or about to attack.
The device - called the wagometer - goes on the dog's back, with sensors attached to its tail.
Details such as the speed, direction and arc of the wag can then be analysed to judge how the dog is feeling.
Ready to attack
"A happy dog tends to have a wide and horizontal wag," said Dr Mugford.
"A very high tail that only wags at the tip indicates the dog is ready to attack.
"The tail is a very important signalling device to other dogs and it emphasises the importance of keeping the dog's tail and not having it docked."
Dr Mugford has spent many years working with dogs and retrained Princess Anne's bull terrier Dottie after it bit two boys in April last year.
'Waggiest' tail judged
The centre he founded in 1979 has become a leading site for the treatment of unwanted behaviour in pets.
The wagometer will be launched in public at the Wag and Bone Show, taking place at Ascot Racecourse in Berkshire in August.
The event has been organised by some of Britain's dog welfare charities.
Dr Mugford said his device would help judges decide which dog has the 'waggiest' tail and which is the happiest.