Dogs who trained a long gaze on their owners had elevated levels of oxytocin, a hormone produced in the brain that is associated with nurturing and attachment. After receiving those long gazes, the owners’ levels of oxytocin increased, too.
http://well.blogs.nytimes.com/2015/04/16/the-look-of-love-is-in-the-dogs-eyes/?smprod=nytcore-iphone&smid=nytcore-iphone-share