That's one.

As a child my grandfather would tell me story of his great great grandfather's Ignacio crossing the desert in Mexico. He and his wife rode in a covered wagon pulled by donkeys. A few hours into the journey one of the donkeys tripped, and he said, "That's one." Few hours go by and the donkey trips again, and he says, "That's two." Hours go by and again the donkey trips. Ignacio says "That's three." He pulls out his gun, shoots, and kills the donkey.

At this point his wife starts yelling, " What were you thinking! We don't have many donkeys! Why would you shoot him!" Ignacio replied, "That's one."

Edit: one too many s's.