Dead as a Door Knob?

This has nothing specifically to do with living here, but it is a funny story. We went to the capital city of our country to visit our friends Paul and Natalie and to go eat TGIF before we move even farther away from it. We were sitting around talking and I asked them if I could borrow an ipod charger because "It's dead as a doornail". Blake corrected me and said "No, Carol it's 'Dead as a Door Knob.'" His reasoning was that there is no such thing as a door nail. It started a friendly debate with Paul and I arguing for the door nail and Nat and Blake arguing that it was a door knob. We decided to settle the debate by googling the expression. Natalie found an etymology website and typed in "Dead as a..." and both expressions came up. She clicked on the "Door Knob" link and it said:

"Dead as a Door Knob. Etymology: possible from misinformation or a misunderstanding or the phraise 'Dead as a Door Nail'."

We laughed pretty hard. Turns out door nails were a well-known item when Shakespeare made up the phrase!