I have a theory it is down to the amount of mud we encounter.
Of course my dogs don't go on the sofas, funny how their hair gets on them though. Could that be the sound of paws hitting hardwood I hear when I come in the door?
Not everyone follows my rules, I guess we are fairly democratic as a family, but I draw the line at giving the dogs a vote!
At the moment it's a hair/titty milk (post-season, not preggers)/claw marks/slobber combo.. no willy snot (smegma.. yuck) currently but I have no doubt more will be along shortly..