You shouldn't tie that...

is what I was told while at the grocery store when referring to a bag of produce I had.  "You shouldn't tie a knot in that bag. It makes it weigh more."

... wat ?

At what point did the fundamental law of conservation of mass become a thing of the past?  I mean it's not something that's all that new.  My favorite question to ask when I was out and about (at fast food restaurants) was if they accepted Hawaiian money (which most of the time they didn't).  I think I just might replace that (or at least add it) with asking grocery store checkout cashiers if it's better to leave plastic bags open or tie them when weighing.

Why are people so fucking dumb sometimes?