A man is near two cows, one white, one black.
A passerby asks him:
"What is their value?"
"The white one 1000$"
"And the black one?"
"The black one too"
"And how much milk they produce every day?"
"The white one ten liters"
"And the black one?"
"The black one too"
"And how much food they eat every day?"
"The white one thirty kilograms"
"And the black one?"
"The black one too"
"Excuse me: when I ask you something about those cows, why do you answer about the white one only?"
"Because the white one is mine"
Spoiler
"And the black one?"
"The black one too"