Here’s the rule: “Who” refers to people, “that” refers to everything else. So you say,
The person who sits next to me stinks.
Not
The person that sits next to me stinks.
Okay, maybe you shouldn’t say either sentence, but you get the idea.
I ran into an exception that works. Maybe we could call this personification. After all, aren’t dogs really people?
Besides, Mike Peterson, of Comic Strip of the Day is a dog person, so maybe that’s a good excuse, too.
PS—Unrelated bonus article: I don’t do politics here, but this appeared yesterday in The Washington Post and it’s about an English teacher correcting someone’s writing. I guess I gotta be proud.
https://www.washingtonpost.com/news/education/wp/2018/06/01/trump-sent-a-retired-teacher-a-letter-about-gun-policy-she-fixed-the-grammar-and-sent-it-back/?utm_term=.bdb58b698ae6