A friend, Dave, was a cattle rancher in Alberta and had three mules which he raced for fun. A white one, a light grey one, and a black one.
One day my friend and I drove into "Dave's" yard and saw the white mule and the black mule standing around in a field. Since the three were always together, we looked around and finally spied the light grey mule, lying flat on his side, sleeping in a dust wallow which the mules had made. He was the same color as the soil and very hard to see.
Dave came out and met us at the vehicle, where we talked about various things, until a lull in the conversation allowed me to ask, "Those are your mules in the field, right, Dave?".
He looked a bit surprised as I had seen them many times, but I proceeded, "I see your white mule, and your black mule, but what is in that depression in the field? <pointing to the light grey mule>.
He responded, even more perplexed, "It's my grey mule!".
I turned to my friend and said, "See, Ross, I told you that the neighbors were wrong about Dave!'.
By now, Dave's really wondering what's going on, and he asked, "What's this about?".
I said that it was obvious that the neighbors were wrong when they said that he didn't know his buttock from a hole in the ground.
Sometimes it can take 1/2 century of attention to find the opportunity to use a line like that.