The Show Where Woody Shows Up - S6-E13
Revealing mistake: Frasier and Woody look at the Seattle tourism book, and in particular a photo of the city. However, you can see there may be some text on the page, but there certainly isn't a photo.

Starring: Kelsey Grammer, David Hyde Pierce, John Mahoney, Jane Leeves, Peri Gilpin
The Show Where Woody Shows Up - S6-E13
Revealing mistake: Frasier and Woody look at the Seattle tourism book, and in particular a photo of the city. However, you can see there may be some text on the page, but there certainly isn't a photo.
Visible crew/equipment: When Frasier is standing through his sunroof to speak with the drivers stuck behind him in the parking garage, one shot shows Frasier's body and much of the rear window which features a very clear reflection of the boom mic.
Selling Out - S1-E9
Frasier: Roger, at Cornell University they have an incredible piece of scientific equipment known as the Tunneling Electron Microscope. Now, this microscope is so powerful that by firing electrons you can actually see images of the atom, the infinitesimally minute building blocks of our universe. Roger, if I were using that microscope right now, I still wouldn't be able to locate my interest in your problem.
Chosen answer: The turkey's stuffing.