Aww, the cuties on jello! Most likely, Sam’s not gonna bounce on jello. He’s small, but he’s the much heavier of the pair, and he wears his strong little boots. Oscar, on the other hand, is practically weightless. His cloth wraps around his feet make him a much better ninja (against anyone but Dean!), so as long as you don’t tell him jello is food, he’ll bounce away and wobble around.
Of course, if you tell him it’s food, he’ll be much busier eating it to bother with bouncing.