Cats: For the new experiment, ten dogs and ten cats had saliva samples taken before playing with their owners for ten minutes. Afterwards, another saliva sample was taken and tested for the presence of oxytocin.

The results were astonishing: dogs showed an average increase in the hormone of 57.2 per cent, but cats just 12 per cent.

‘From this sample it’s true to say that these dogs love their owners five times more than the cats do,’ says Dr Zak.

‘I was really surprised to discover that dogs produced such high levels of oxytocin.
‘It was also a nice surprise to discover that cats produce any at all. At least some of the time, cats seem to bond with their owners.