I went with a friend to buy a grey cotton sweatshirt.
I bought one but when I got home I noticed a little rip in the left sleeve. I showed it to my friend who encouraged me to return it.
Would you believe, when I got to the store, the salesperson said "I'm sorry. This isn't the sweatshirt you purchased. Our records indicate that the sweatshirt you bought was 80% rayon and polyester. We can't take back this cotton one."
"I'm afraid you're wrong", said I, smiling at my friend, who had been with me through the whole affair. "I did indeed purchase a cotton sweatshirt." I pointed to my friend.
"This is my material witness".