Nadia Croes and her ex-boyfriend broke up last November after 10 years together, and their seven-year-old pit bull, Mia, was a central battleground in the split. "When we would fight toward the end, I would joke, ‘You can’t have the dog,’ like how other people might argue about a flatscreen," Nadia says. "He walked and fed her more than I did, because his hours were more conducive to taking care of her, but it was my decision to get a dog and she was always licensed in my name. She’s my baby."

Ryan and his ex-wife worked out a visitation system that allows him to see the two cats whenever he likes, but the split and subsequent move have affected them. "They’re littermates, and they used to be really close friends, but now Smacky fights with Bucky constantly and won’t let Bucky get near him," he says. "Smacky is not happy. He’s a child of divorce." 

And while couples may have the best of intentions regarding their behavior in the event of a split, reality can intervene; Nadia and her ex-boyfriend had settled on visitation, but his infidelity put an end to that amicable agreement. "This isn’t to spite him or hurt him, but he screwed up, and one of the things you lose is your ability to see your dog," she says. "He has in e-mails mentioned wanting to see Mia, but the circumstances are different now and I do not want to see or speak with him."

While state legislators in Michigan and Wisconsin have recently introduced laws to bridge the gap between family member and possession for couples arguing over pets, most U.S. states still have no firm rules about the issue, says Favre. "Some judges feel there’s no law that allows them to take into account the best interest of the animal, and they are constrained to do anything but treat them as property." Despite that constraint, pet custody cases have spanned the globe in recent years, popping up everywhere from South Africa to Australia and China, where a court ruled earlier this year that a woman could visit her Pekingese, Beibei, twice a week if she pays support to her ex-husband. Pets are more likely to be treated as property by courts if they are particularly valuable or unique, Hennenhoefer says, such as a purebred or show animal.

For pet owners moving on with their lives, introducing a new flame to a pet, as Gyllenhaal did with Witherspoon, can hurt the ex even more than the new boyfriend or girlfriend. "My ex-wife is seeing someone else now, so that upsets me that he’s stepping in and taking my place with the cats," Ryan says. "It’s ridiculous, but it’s true. I feel like they’ve got a stepfather now, and I don’t really like that."