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two men in suits and ties are standing next to each other . one of the men is wearing glasses and a bow tie .
Alt: The scene from “Singin’ in the Rain,” right before the musical number ‘Moses Supposes.’
The elocution teacher is demonstrating the Moses Supposes tongue twister, and he’s way too excited about it. Cosmo Brown (played by Donald O’Connor) is standing just behind him and acting a fool, making silly faces behind the elocutionist’s back, managing to placidly arrange his face as the elocutionist turns to look at him at the end of each phrase.
Now we get to the actual moment of the gif. It’s the last phrase of the tongue twister (“[as Moses] supposes his toes-es to be”), and Cosmo is making his silly faces behind the elocutionist’s back. The elocutionist excitedly turns to face Cosmo on the tongue twister’s final word, but instead of a neutral, normal expression, Cosmo has lost the plot and makes a silly, exaggerated sort of buck tooth face. They hold for a beat, presumably somewhat startled by the whole thing, then Cosmo fixes his face while the elocutionist pulls back, affronted.
Aaaaand scene.
(In the film this leads directly to the start of the ‘Moses Supposes’ number, which is a fantastically choreographed tap routine of controlled chaos and well worth the time to find the clip of and watch.)
(“Aaaaaaeeeeee!”)