The demonstrators for votes for women are referred to as "suffragettes." That was the American term; in Britain they were called "suffragists."
In the Hyde Park sequence, when Abbott and Costello fall through the pothole, the carpet covering the pothole is clearly visible as they try to pull themselves out.
When Costello was standing by the mannequin of George Washington, the mannequin blinked.
This movie is set in the 1890's, but the Dracula/Frankenstein dummies in the Wax Museuum are the Universal portrayals from the 1940's.
When Mr. Hyde is pedaling behind a woman's tandem, she is an older lady. There is a camera cut showing her as she falls down; she gets up without camera cuts and faces the camera in full view: she has transformed into a younger actress/character---her stuntwoman.