A computer programmer leaves work and heads for home. Being the good husband that he is,  he calls his wife and asks if there's anything she needs him to pick up on the way.
Yes, a gallon of milk and, Oh, if they have eggs, get a dozen.
Later he arrives home and stumbles into the kitchen burdened with a dozen gallons of milk. His wife, perplexed, asks him ``why in the world did you buy 12 gallons of milk?''
What did he answer?

ANSWER: They had eggs.

EXPLANATION: 

Yes, a gallon of milk and, Oh, if they have eggs, get a dozen.

intepreted as

IF they have eggs THEN get a dozen gallons of milk.