Super Mario Bros.: Jumping over the flag

In Super Mario Bros., it is possible to jump over the flagpole in some levels. The flagpole is supposed to be the end of the level, but by jumping over it, the level does not end, but goes into a loop.

What levels can I jump the flagpole?
Levels:


 * World 1-1


 * World 3-3
 * World 7-2
 * World 2-1

Credits and acknowldgements

 * Wikipedia


 * YouTube

Links

 * http://www.youtube.com/watch?v=OQ9LOCf1bJQ - over the flagpole in World 3-3


 * http://www.youtube.com/watch?v=0ZJaKNhqlIA&mode=related&search= - a hacked game to show what's over the flagpole in World 1-1.

Happy Glitchin' :)