On opposites

During reading time today, after reading a book on opposites:

Me: "Colin, can you tell me what the opposite of big is?"

Colin: "Small."

Me: "Great! Can you name something that is big, and something that is small?"

Colin: "A monkey is big...and a bird is small."

Me: "Great! And, what is the opposite of the same?"

Colin: "Different."

Me: "That's right! Can you tell me two things that are different?"

Colin: "Yep...you and I are different."

Me: "That's right. You and I are very different. We are different in many ways. Can you tell me one reason why we are different?"

(And so my thought process begins for him: you are a girl and I am a boy....you are big and I am little....you are tall and I am short...)

Colin: "We are different because....{thinking}

....because we have two different heads."