Level 5 : the different colour..
level 6 : circle
level 7 : '?'
level 8 : level 8
level 9 : side up
level 10 : read the text :D
level 11 :''N'O'W''
level 12 : wait some seconds :D
level 13 : its easy
Level 14 : ....easy too
Level 15 : do you look the strange in 'level 15' ? find the stop button ..
HOPE it HELP YOU :D