Wrong Nails

Dum and Dummer were roughing in a house when Dummer sees Dum throwing away half the nails.

- Hold it! - says Dummer.

- Why are you throwing all those nails away?

- Because. - says Dum.

- The heads are on the wrong end.

- You dummy! - replies Dummer.

- Those are for the other side of the house!