Loving the game, Aga, just got some heads up things in case you are unaware.
In world 2-1, the background has some minor graphic hiccups when you head left towards the ship part, nothing really outrageous, just some minor twitches.
And at parts it is possible to stand on the walls without sliding down, I was able to do this after getting the ship part in 2-2.
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http://i1024.photobucket.com/albums/y306/greenseafoam/idunno.jpg
http://img.imgcake.com/zoidberg2re.gif