...as recalled by Dr. Paul Witty who knew Dr. Einstein and it goes like this:
Professor Einstein went to a party one night and the hostess said, "Professor Einstein will tell us the meaning of realitivity."
"I will tell you a story instead", he said.
"I was going down the street the other day with a blind friend and I remarked that I should like a glass of milk. "What is milk?", asked my blind friend.
"A white liquid", I answered.
"Liquid I know, but what is white?"
"The color of a swan's feathers."
"Feathers I know, but what is a swan?"
"A bird with a crooked neck."
"Neck I know, but what is crooked?"
By that time I had grown impatient and I seized his arm and bent it and I said, "This is crooked". Then I straighten his arm and said, "This is straight."
"Awe", said my blind friend.
"Now I know what you mean by milk."