Boy was milking his cow

Asmall farm boy was milking his cow when all of a sudden a bull came charging towards him. As horrified workers nearby watched, the boy calmly continued his milking. To everyone?s astonishment, the bull stopped a few inches from the boy, turned around and walked away . ?Weren?t you afraid?? one of the workers asked the boy. ?Not at all,? the boy replied , ?I knew this cow was his mother-in-law.?