Mickey's Choo-Choo (1929) 16mm (Patreon)

Here's another public domain Mickey Mouse cartoon. It's a 16mm dupe.Something interesting about this film is the similarities that are shared with the 1930 release Box Car Blue's (Bosko). In particular the gag of a cow being smashed into a tree by a runaway train. Does anyone know where this gag first originated? Harman and Ising reused gags from their work on the Disney Oswald's (see here), but I don't recall an Oswald gag like this. H-I never worked on Mickey mouse, but I don't think they would have blatantly taken an idea from earlier Mickey cartoons that they themselves had not previously done.