This is the direct adaptation of Erle Stanley Gardner's 1952 novel, ''The Case of the Grinning Gorilla". Most PM episodes were original screenplays 'based on characters created by...', but this is an actual ESG novel.

True Boardman makes his only acting appearance here on Perry playing the morgue attendant. Not only was True Boardman his real name, his father was also named True Boardman. True Boardman began his acting career at the age of 3 in 1912, and this was his first appearance since 1936. True Boardman is best known as a writer. At the time of this broadcast, he had already written two episodes of Perry, TCOT Ancient Romeo, and TCOT Lawful Lazarus. Submitted by PaulDrake 33, 18 August 2009.

Lurene Tuttle makes her fifth of six appearances here as Miss Kempton. She was one of the great character actresses in films of the day, and a great favorite of Raymond Burr's She made memorable appearances in "Psycho" [1960], "The Fortune Cookie" [1966], and in the short-lived CBS sitcom "Father of the Bride" [1961] She was wonderful in TCOT Substitute Face, from Season 2. dwhite 1.21.13
+ Funny how the defendant Miss Kempton, is missing from the final scene. Must be that statement she made about being mixed up with lawyers in the previous scene when she was leaving with the police. Submitted by HamBurger, 7/11/2020

And Gavin MacLeod, whom millions remember as the Captain of "The Love Boat" in the 1970s. dwhite 1.21.13
+ As well as Murray Slaughter from "The Mary Tyler Moore Show". olef641 6/14/17.
++ Also as Joseph 'Happy' Hanes on McHale's Navy. Submitted by HamBurger, 7/11/2020

Robert Colbert played Dr. Doug Phillips on "The Time Tunnel" SCI FI Classic from 1966-67. Mike Bedard 2.4.15

Uncredited Actors: Don Anderson is in uniform once again as a Sheriff’s deputy. I think he’s one of the men who hurry past Mason and his client as they escape the gorilla, and he’s definitely the deputy who steps out beside Paul Drake after overhearing the blurted confession of Fallon and Hershey. Submitted by FredK, 2 December 2010.

It’s quite a coincidence that bon vivant Victor Buono should play the personal assistant to a kooky anthropologist when later in Batman he would play an anthropologist himself—one who was hit on the head and thought himself King Tut reincarnated. Submitted by gracenote, 5/4/2011.

Sightings: As Perry grumpily requests Della to carry her own packages in the opening scene, a hatted Distinguished Gentleman (whom we’ve designated as #1) pops out of the phone booth. Submitted by gracenote, 5/4/2011.

Once again, Ray Collins receives billing for Lt. Tragg but makes no appearance. Submitted by gracenote, 5/5/2011.

Murder Method: Of approximately 34 victims that died by stabbing, Benjamin Addicks was the third known to have been killed with scissors (165 and 193). In many of the stories the instrument wasn't identified. Submitted by H. Mason 5/2/15

This is the only credited PM appearance for Hungarian-born Janos Prohaska (Gorilla), who made a career performing inside animal suits...MikeM. 3/1/2017

+Star Trek Alert: Prohaska went on to play various aliens and monsters in the original series Star Trek, including Yarnok, the rock alien, as well as the Horta. He played two gorilla-like creatures in the Trek universe, including a risible venomous single-horned albino primate called a Mugato, in "A Private Little War," which almost kills Captain Kirk. While he played apes before Perry, his speciality of portraying homicidal hominids, or at least ones accused of such, starts here. Submitted by MyFavoritePolarBear, 12/1/22.

That staircase set makes its umpteenth appearance.

The sound of the typewriter does not synchronize with Della's finger action.

A rare episode with no courtroom scenes. DOD 3/6/18

This is the only PM appearance for Charlene Holt (Helen Cadmus), who was a semi-finalist in the 1956 Miss USA pageant as Miss Maryland...MikeM. 3/7/2018

This is the second of two PM appearances for Harvey Stevens (Benjamin Addicks), a veteran of stage, screen and television. After his retirement from acting, Harvey Stevens continued his hobby, flying gliders...MikeM. 5/11/2018

This is the fifth of six PM appearances for Bartlett Robinson (Sydney Hardwick), who was one of the actors who voiced Perry Mason on the radio...MikeM. 7/11/2018

Theme Music: after a number of weeks during which the closing credit theme music was horribly mangled, we return to something approaching the "Park Avenue Beat" theme we all know and love. Submitted by catyron, July 13th, 2018

Set decoration: The return of Carl Biddiscombe to Set Decoration marks an end to such horrors as the Roving Rolodexes seen last episode. Submitted by catyron, July 13th, 2018