All-Star Cast: The first film to do such a thing. Beforehand it was considered wise to only put two big stars in a film, to minimise production costs. This put five of MGM's top stars in a film, and thus became the Trope Maker.
The reason Wallace Beery signed on? He was told he'd be the only one in the cast that got to use a German accent.
Method Acting: Greta Garbo got so into the kissing scene that she kissed John Barrymore for a full three minutes after the director called for cut. Incidentally Garbo and Barrymore ended up getting on very well, despite being wary of working with each other.
Most of the stars actually turned down their roles at first—Greta Garbo not thinking she was young enough to play a prima ballerina, Joan Crawford not wanting to wear the one outfit for the whole film, etc. But they were eventually all persuaded to sign on.
Buster Keaton wanted to make an Affectionate Parody set in a New York flophouse called 'Grand Mills Hotel'—with himself in the Lionel Barrymore role, Marie Dressler as the ballerina, Jimmy Durante as a bogus count, Oliver Hardy as the industrialist, Polly Moran as the secretary and Henry Almetta as the hotel clerk. Irving Thalberg wanted to make it, but Keaton had been fired by MGM and didn't wish to return. Marie Dressler would later star in the Spiritual SuccessorDinner at Eight.
Irving Thalberg wanted Norma Shearer to play the secretary role. However, she got mountains of fan mail telling her not to do it, so she declined.