In his study, Zak tested blood samples collected from 10 dogs and 10 cats before and after they had some playtime with their humans to measure the level of oxytocin in the animals. As the neuroscientist told HuffPo, humans produce varying levels of oxytocin when experiencing positive interactions and levels of 50% or more when interacting with someone we truly love. Apparently, the same applies to dogs, and the ones he tested produced more than 52%. However, the tests showed that cats produced just 12%, and half of the cats in the study didn't produce any oxytocin, according to the report.
“So your dog really loves you … a lot,” Zak told the publication. “But what makes this so amazing is that the oxytocin they produced is for another species, not their own. The fact that this is cross species is really freakin’ crazy/cool. Their brains are telling them that they love us.”