Enter one of the following initials at the high score screen, then start a new game to unlock the following items and effects.

Beer mug (pizza instead of bubbles)
Enter KTT as initials.
Flamingo (pink worms instead of bubbles)
Enter STR as initials.
Fork (enemies turn into fruit)
Enter SEX as initials.
Knife (enemies turn into various items)
Enter ... as initials.
Octopus (wooden stakes instead of bubbles)
Enter TAK as initials.
Soda can (enemies turn into various items)
Enter I.F, KIM, MTJ, NSO, or YSH as initials.