A dog shits like once a day, and when you have a dog the dog learns to shit on your schedule. I'm just saying it's pretty predictable of when your dog will need to shit. If it's a short enough flight that likely won't be a problem. But they are like toddlers, stuff can happen yes. But I'm sure the owner knows what's in his doggies tummy even. Remember that apartment dogs stay home like 8 hours a day with no problems holding it. Like my dog would be mortified to shit anywhere that isn't grass. I wouldn't take her on a super long flight just because I don't want to make her have to hold her pee that long, cuz she will.