So This is How Sinatra Felt - S6-E12
Plot hole: Bud and Kelly hide behind the cash register all day. They talk normally the whole time yet Al doesn't hear a word they say and has no idea they are even there.
Plot hole: Outside the Savoy, Marcy tells Jefferson that at last, they found the Bundys. How did they know that the Bundys were there? The Darcys had not been in touch with them since they were left behind at the airport, and the Bundys only decided much later that they were going to the Savoy.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.