Cinnamon sets her handkerchief down on the floor of the basement for the guards to discover, but when they find it, it is in a different position.
During the playing of the mission tape, the close-up of the take-up reel shows very little tape has accumulated on the reel. Wide shots before and after show much more tape on the take-up reel.
Willy and Barney are both wearing welding goggles with dark lenses. When they are shown in closeup the lenses are clear glass so that their eyes can be seen.
Greg Morris barely keeps it together and tries not to laugh as Peter Graves is saying his line, impersonating "Chief Gorsinsky" with a funny Eastern European accent.
As Mr. Phelps enters the industrial shop at the beginning of the episode to listen to his self-destructing tape, he carefully looks around to make sure no one is watching, but misses the crew member clearly visible for several frames in the left side of the screen wearing a short sleeve white shirt and hat.
Willie and Barney do a lot of welding to take apart and re-weld the sculpture. This would give off heat and an obvious smell, but neither guard notices anything when they come in to do a security check.
As for the heat: that's why Cinnamon turns up the heat in the building - to mask the heat generated by the work Willie and Barney are doing.
As for the heat: that's why Cinnamon turns up the heat in the building - to mask the heat generated by the work Willie and Barney are doing.