First "Walt Disney" movie of Dean Jones (F.B.I. Agent Zeke Kelso), who went on to star in numerous "Disney" projects throughout the 1970s.

The Seal-Point Siamese cats who collectively played the role of D.C. in this movie were all "traditional" Siamese, as opposed to their more streamlined contemporaries. Amongst fanciers of traditional Siamese, they're affectionately known as "Appleheads".

This Hayley Mills' last "Disney" movie of the 1960s, and her last juvenile role. Her next "Disney" role was in "The Parent Trap II (1986)." The remake, "That Darn Cat (1997)," was Christina Ricci's last "Disney" role.

In the original 1963 novel, "Undercover Cat", "D.C." stands for "Damn Cat".

In the French-dubbed version, D.C.'s name is "P.V.", which means from french translation "Petit Voyou": Little Delinquent. Which would put another apparent name: Delinquent Cat.

When Patti Randall (Hayley Mills) meets Agent Zeke Kelso (Dean Jones) for the first time in his F.B.I. office, she says that her father named the cat. She says her father called the cat "something much worse" than "darn", but her mother wouldn't let them use that name. The inference is that Patti's father named the cat: "Damn", from Gordon Gordon and Mildred Gordon's novel, "Undercover Cat", upon which this movie was based.

Patti's dislike of surfer movies is likely a cheeky reference to A.I.P.'s concurrent "Beach Party" movies, reflecting Walt Disney's discomfort of his star Annette Funicello appearing in them.

The 1964 Mercedes 230 SL that appeared in the film as Roddy McDowall's car was actually Walt Disney's personal car. Disney rented his car to the film for $100 per day, possibly because he felt guilty about buying himself such an expensive car. The Disney family still owns the car to this day.

At the drive-in theatre, ticket-taker Burton was ordered to chase D.C. away by the drive-in manager. Burton's chase of D.C. ended when he fell into a Volkswagen with an open top which held two mannequins, one dressed as a male and the other one dressed as a female.

The tracking transmitter collar that the F.B.I. Agent puts around the neck of D.C. is shown in a close-up with all of the electronic components exposed. There is one diode, two resistors, two capacitors, and one wire coil. The device as shown could never actually transmit anything, because there's no active transmitting components on the circuit board, such as transistors.

"Diabolically Clever!", "Diabolical Cat!" and "Delinquent Cat!" could be three substitute nicknames for D.C. Patti Randall specifically said "D.C. is really "diabolically clever" to F.B.I. Supervisor Newton, on Friday evening, just before Margaret Miller was successfully rescued. D.C. did cause ruckuses almost throughout the movie.

Canoe Henderson (Tom Lowell) mentions "going to a drive-in theater Thursday evening". This movie was released Thursday, December 2, 1965.

Patti Randall (Hayley Mills) said "Darn Cat" once, when she first met FBI Agent Zeke Kelso (Dean Jones) and brought Margaret Miller's (Grayson Hall's) wristwatch to the F.B.I. building. Second rated criminal, Iggy (Frank Gorshin) slowly says the movie title, "that darn cat!" (in approximately six to nine seconds), as he was being arrested. Bobby Darin musically sang "darn cat" ten times in the introductory song and sang "darn" once in the closing song. Bobby Darin sang "darn" eleven times total, in the opening and closing songs and "Darn Cat" was said or sang twelve times total.

The movie stars four Academy Award nominees, Grayson Hall, William DeMarest, Elsa Lanchester, and Ed Wynn.

Frank Gorshin and Liam Sullivan were both on pivotal episodes of "Star Trek" (1966), Sullivan in season three, episode ten, "Plato's Stepchildren", often credited with being the first television interracial kiss; and Gorshin in season three, episode fifteen, "Let That Be Your Last Battlefield", a sharp commentary on racism.

D.C.'s two initial name was said forty-two times total in this movie, thirty-seven times by Patti Randall, three times by F.B.I. Agent Zeke Kelso, one time by Ingrid Randall, while reading newspaper, morning after Zeke Kelso and the F.B.I. found the two criminals and apprehended them. The first time was by Canoe Henderson, while waiting for the evening surf weather. Patti Randall once told Kelso that D.C. stands for "Darn Cat", inside the F.B.I. office. Kidnapped bankteller, Margaret Miller put her wristwatch around D.C.'s neck, the previous evening and Patti discovered it, as she was feeding D.C. and feeling around his neck, to slowly stroke or scratch D.C.'s neck.

Three celebrity names were mentioned once, two by FBI supervisor Newton. Newton mentioned Mack Sennett and Chester Conklin the morning after the first evening, when FBI agent Zeke Kelso had four agents, Spires, Graham, Kelly, and Cahill follow D.C. Two days later, (the morning before kidnapped bank teller Margaret Miller was rescued), jeweler Hofstedder mentioned private investigator Eliot Ness' name.

Dean Jones' lifetime: Sunday, January 25, 1931 to Tuesday, September 1, 2015, was 30,900 days, equalling 4,414 weeks and two days.

When Iggy first thinks that he and Dan stole $250,000 from the bank, Dan tells him the amount is $160,000. Iggy then went to their gagged bankteller, Margaret Miller and asked her. After asking if it was $250,000, she shook her head no. Iggy then asked if it was $200,000, she shook her head no again. Then, when he asked if it was $160,000, then she nodded her head yes. (Iggy threatened to hit Margaret with a right hook, but Dan stopped him). The amounts of Iggy's first two guesses decreased each twenty percent, exactly.

The phone number to F.B.I. Supervisor Newton's office is 626-0025.

F.B.I. Supervisor Newton's phone number digits add up to twenty-one.

When agent Kelso is addressing the other agents about following DC the cat he partially quotes the bible, Ruth 1:16, where the Moabite girl Ruth tells her mother in law Naomi, "wherever you go, I will go". Agent Kelso says, "whither thou goest, you will go"

When Ingrid Randall's (Dorothy Provine's) current boyfriend, date, and especially car pool, and next-door neighbor Gregory Benson (Roddy McDowall) stormed in the Randall's house carrying his shotgun to chase down F.B.I. Agent Zeke Kelso (Dean Jones), at the time, Gregory was wearing a monogrammed bathrobe with three capital initials, G J and B, the three initials are of his character role name, "Gregory J. Benson". As this movie concludes, Ingrid has Kelso as her new date or boyfriend and car pool.