Accidents will happen...

During the filming of The Great Dictator (1940). 

While filming one of the ghetto scenes with Paulette, Chaplin's left hand was caught in a slamming gate, breaking his middle finger.

"Leading lady (and Mrs. Chaplin) Paulette Goddard quickly called a car and rushed Chaplin to Hollywood Hospital, where they found themselves completely ignored by the hospital doctors & staff. After an interminable wait, Goddard approached a doctor and said that Mr. Chaplin's case needed immediate attention. The doctor looked more closely at Chaplin and his finger, then immediately apologized, stating, according to the original press book of The Great Dictator, 'When I saw you both coming in in makeup, I thought it was a couple of Hollywood jokers having a little fun at our expense.'" (Hooman Mehran, "Second Thoughts On The Great Dictator," Chaplin: The Dictator & The Tramp, BFI, 2004)

Watching the film closely, you can see Chaplin favoring his finger in certain scenes, including the one right before the gate closes, which suggests that he reshot this scene after the accident.

You can clearly see a bandage on Charlie's finger in the coin-eating scene.

And at the October 1939 funeral of Ford Sterling.

L-R: Harold Lloyd, Mack Sennett, Barney Oldfield, CC, Douglas Fairbanks, Donald Crisp and Charlie Murray.

During the filming of Easy Street (1917).

In the scene where Charlie pulls the lamppost down on the bully (Eric Campbell), the lamp's sharp metal edge cut across the bridge of his nose requiring stitches. The injury contributed to a delay in the release of the film.

During the filming of The Circus (1928).

Chaplin told journalist Egon Kisch in 1929 that he was scratched so badly by the monkeys while filming the tightrope scene that he had to be under a doctor's care for six weeks. Kisch noted that Chaplin had "two clearly visible wounds." (Egon Erwin Kisch, "I Work With Charlie Chaplin," 1929)

During the filming of The Idle Class (1921).

In his autobiography, Charlie mentions a "slight accident" with a blowtorch while filming the scene below. "The heat of it went through my asbestos pants, so we added another layer of asbestos." (My Autobiography, 1964)

Naturally, the press took this story and ran with it.

Capital Times, May 11, 1921

The "studio hospital"? Must have been next to the Chaplin Studio restaurant.
Adding that Edna "helped smother the flames" was a nice touch at the end.