Joey Bishop is shown filming a commercial at his used car lot; across the street is a building with a large clock showing 1:02. When he and Elizabeth Montgomery are talking a few seconds later, the clock is showing 12:20.
When Johnny and Dare last part, they agree to meet "tomorrow night, 7:00 at The Real Tony's". The next morning Dare says "he'll be in a restaurant called The Real Tony's 7:00 tomorrow night" but it would actually be that night.
When Dare is on the yacht and starts to dance the Twist, the drink she had in her hand disappears - but she holds onto her cigarette.
In the second half of the film, after Darien abandons her car in front of the beauty parlor, the police show up. The police later describe it as being a "1961 Ford". It is in fact a 1962 Ford (Galaxie 500 Sunliner).
At the start of the movie, the Germans shoot Salvatore Giordano from a Jeep. Unless they stole the Jeep from the Allies, it should have been a German vehicle.
When Suzy runs off to get Bill on the yacht after Dare confesses what she did with Johnny, the background moves after Suzy runs past, revealing it to be a photo backdrop.
When Henry Silva meets Telly Savalas for the first time in his office the camera long shot is panned out so far that we see Silva's two "marks" (black tape) on the rug in front of the desk, where he's supposed to stand next. Silva walks over and steps on both marks before it cuts to the close ups.
At the Italian airport - when passing the European weather board - the temperatures are presented in Fahrenheit; that or it is 50C or warmer in Europe (about 122F).