For a first flash this was pretty good. It started out well and remained funny for the rest of the flash. The various plan method of opening the box is nothing original, but you still managed to make some of the scenarios funny. I also liked the numbers given to each attempt. The sinister then somewhat anti-climatic was probably the best bit for me.
In terms of animation the flash also doesn't score too badly. It wasn't perfect as you could occasionally see where the shading lines entered the outline which made it look a bit messy. The animation itself was a bit wobbly, but still looked good.
Keep up the good work and I'll look out for episode 2.