There are 5 bunny pictograms to find.

Click 555 times on the bunny pictogram in the top left of this screen:

The game has six speedrun achievements that require finding all helmets in under 10 min / 5 min / 3 min / 2:30 min / 2 min / 30 sec respectively.
One playthrough is enough to obtain all of the above.

Once gameplay starts (after the flashing alert), immediately press ESC and, while the game is paused, click on all helmets you see on the current section of the level.
Resume the game by pressing ESC once more, scroll down to the next screen and pause again.
Be careful not to accidentally press the restart or quit buttons in the middle of the screen.
Repeat until you find all 100.