A young man's grandmother was turning 80 and had moved into a new flat. He wanted to drop by, see her new place, and wish her happy birthday.

He called her and she instructed him as follows:

"Park in front of the building and come to the main door. You'll see a big panel on the right. With your elbow, push button 115. I'll hit the buzzer and I'll let you in. Walk inside and turn right for the elevator. Get in, and with your elbow press number 115. Walk out of the elevator and turn left. Come down the hall to 115 and ring my doorbell with your elbow."

"Grandmother," he says. "That's easy enough, but why the heck am I pushing all these buttons with my elbow?"

"What?" she replies. "You're coming empty handed?"