Location: In the scene where Paul is on his way to W. L. Picard’s office, two California state highway signs can be seen, one for route 23 and the other for route 118. These roads actually converge in the city of Moorpark, not in the “Pinon City” of the show. See here. Submitted by Steve Fox, 10/7/2004.

That Mysterious Black Bar that appears in the scene with the roadsigns is there to cover up a sign. More here. From a post to the Perry_Mason Yahoo! group by Rich Erickson, 12/16/2006.
+ I scanned this episode on the Perry Mason 50th Anniversary DVD for the scene of the Mysterious Black Bar and find that there is no black bar. It looks like the scene has been stretched vertically to eliminate the bar. Tricky! Posted by daveb, 4/8/2008.

Goof: I noticed a blooper in the opening scene. When Adam West looks at the registration for the truck, it says it is a “Ford Pickup.” In the next shot, when the truck pulls up it can clearly be seen that it is a GMC truck. Submitted by J Fleming, 12/31/2009.

In another entry of TCOT All-Purpose Address, the above truck registration indicates that Fred Swan is yet another resident of 1040 N. Las Palmas in LA (also used in episodes #78, #89 and #100). As daveb mentioned, Hollywood Center Studio is the long-time tenant of that address, and at their website the Mason series appears in the “Featured List” of TV productions filmed there. Submitted by FredK, 1/3/2010. There’s more about this on the Location Trivia page.

Eloise Hardt makes her only Perry appearance here as Marta Wiltern. When I initially watched the episode, I thought she was Barbara Bain, the resembleance is remarkable. In 1968 Eloise Hardt’s only child, Marina Habe, a 17-year-old college student, was kidnapped and murdered. The murder was never solved, but a lot of people believe it had something to do with the Manson crowd. Submitted by PaulDrake 33, 29 January 2010.

Neither D.A. Burger (William Talman) nor Lt. Tragg (Ray Collins) appears in this episode. Collins, however, appears in the credits while Talman does not. Submitted by gracep, 11/8/2010.

Character Names: Although left out of the credits, Miss Sarah’s last name is McKay, and Prosecutor Hale’s first name is Jonathan. The prosecutor refers to a officer named Gene Barr, but it may or may not be the same Policeman in the credits. Submitted by gracep, 11/8/2010; updated 7/7/2011.

Sightings: The food at Mr. Needham’s restaurant in Pinon City must be awfully good, because it lured Distinguished Gentleman #1 from L.A. to the little town. We see him sipping tea and talking enthusiastically to his companion as Iris McKay (Enid James) storms in. One of the few times he is so emotive! Submitted by gracep, 11/8/2010.
+ Read about all our favorite frequent faces and help us spot more! Submitted by gracep, 11/9/2010.

Less than five years after this episode was first shown, Adam West sported a cape in the memorable title role of TV's Batman series, which first aired on January 13, 1966, and ran for three seasons. Submitted by Fifty-Niner on July 12, 2011.

Miss Sarah's "The Machine" appears to be a 1939 Packard Touring Sedan. Car picture here. Observe these Identifying Points: radiator/grill shape, especially across the top, radiator cap/mascot, cased spare wheels on fenders, and windshield shape. Some pictures from the episode here (scroll down to mid-page). Submitted by GaryW, 28 Aug 2011, via email.