Jumbo is alternately using his front feet/back feet between shots when he is dancing on the circus pedestal.
At the beginning there is a stage curtain painted to show the elephant Jumbo. It portrays him as an African Elephant with large ears. The real elephant in the film was an Asian elephant with smaller ears.
Sam's secret performance is the circus's tight rope walker would not be possible as presented. He could not possibly have known the routine, including his entrance with the spotter, nor the act on the wire itself which was cued to the band's musical scores.
In the film's opening shots of circus tents being erected, several five-man synchronized sledgehammer teams busily pound stakes into the ground, yet despite the Herculean efforts of these muscle dudes, the stakes don't sink an inch.
Lulu somehow manages to come out of the cannon backwards - the opposite way to how she entered.