Birthdays

Sometimes the gags just write themselves. D'wife got me a card:

So she posits this question and asks that I tap my cane 3 times if I agree.

Me: What?
Wife: Asks again, louder.
Me, trying to remember which button makes the hearing aid louder: What?
Wife, now about ready to hit me: Asks again, very loud. Yes, I did find the right button.
Me: No cane, bangs knuckles on table slowly, "Knock,   knock,..., " How many if I agree?"