Two Blondes with hammers

Two blondes with hammers, Carol and Donna, were doing some carpenter work on a Habitat for Humanity house.
Carol, who was nailing down house siding, would reach into her nail pouch, pull out a nail, and either toss it over her shoulder or nail it in.
Donna, figuring this was worth looking into, asked, ‘Why are you throwing those nails away?’
Carol explained, ‘When I pull a nail out of my pouch, about half of them have the head on the wrong end, and I throw them away.’
Donna got completely upset and yelled, ‘You moron! Those nails aren’t defective! They’re for the other side of the house!’