So why is it...

I go away for less than a week to do some training for my new job, and I come home and find the dogs are like ten percent heavier then they were when I left? No criticism of my fantastic dog sitters, but how is that even possible? The dog food levels are right where they should be, so I have to wonder how many extra treats did these two get while I was gone, and exactly what kind of good behavior did they exhibit to earn them all? I mean, we're talking Murphy and Belle here...