someone on GT explained this very well a while back, and of course, I don't remember who Anyway, my paraphrasing: as the food moves through the digestive system, a lot of the liquid is absorbed in the large intestine. So, when the dog goes the first time, he's producing what's been through the system and is "ready". If he goes again (and Fletcher poops at least twice on every walk), it's going to be softer because it (the poop) hasn't been in the intestine as long, and all the liquid hasn't been absorbed. So, each poop, assuming the first was normal, will be softer. I know I have put this very unscientifically, but it made sense to me