also you can push the box off in level 4 and get stuck
if you press escape while in fullscreen it just takes you out of fullscreen but if you press escape while out of full screen you go back to the menu so you don't have to like restart the page or anything. Most of level 5 of possible actually, there is just one jump that has 4 lines of spikes in a row and it's just impossible, you can make a 3 spike jump though.