Which pets love their owners more: Cats or dogs?
One BBC2 documentary, titled Cat versus Dog, has actually looked into this - and revealed some interesting results.
For the programme, neuroscientist Paul Zac investigated which species increased oxytocin levels and found that dogs won paws down.
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The results found levels of the hormone increased by an average of 57.2 per cent in dogs but only by 12 per cent in cats.
Oxytocin is known as the "love hormone" because it is released when people cuddle or bond socially.
Dr Paul Zac says: "I was really surprised to discover that dogs produced such high levels of oxytocin... the dog level of 57.2 per cent is a very powerful response. It shows these dogs really care about their owners. 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."