The man finally decided to ask her to marry. She immediately said "yes".
The next morning when he awoke, he couldn't remember what her answer was! "Was she happy? I think so, wait, no, she looked at me funny..."
After about an hour of trying to remember to no avail, he got on the telephone and gave her a call. Embarrassed, he admitted that he didn't remember her answer to the marriage proposal.
"Oh", she said, "I'm so glad you called. I remembered saying 'yes' to someone, but I couldn't remember who it was."