We tend to think of our interpersonal relationships as far more sophisticated and complex than the relationships we share with our pets, but the two are more alike than we'd care to admit.
Both involve choosing a partner, sharing meals and affection, learning to make each other happy and discovering how to communicate those feelings words can't describe.
There are plenty of dog days during these relationships too, as we try to live in the same house without tearing each other apart and struggle to set boundaries in regards to strangers.
But as this comic by Robert Brown shows the main thing both relationships have in common is the crap- the emotional crap, the crappy gifts we buy for each other, and the times we literally come face-to-feces with each other's crap.
See Human Relationships vs Dog Relationships at CollegeHumor (NSFW)