How do I get Critical hits in Fruit Ninja? And what are they?

Well,

1. They are worth 10 points instead of the traditional 1 point for standard fruit.

2. They are perfectly valid in combos like other fruit, the combo points are not multiplied by 10, you just get 9 extra points than if there was no critical hit in the combo.

3. Completely and utterly random. There is no special swiping motion or timing that will get you a critical hit. The game is known to give completely random points as seen in the Arcade mode with the random assortment of power-up bananas.

I imagine they exist for flare. It adds a random element of reward to the game to give it a little bit of extra addiction.

While another answer is fantastic, some things have changed over the years, and there are now different types of critical hits.

With the standard critical hit being well outlined above, the others are:

Critical +25

These criticals appear when the Shiny Red Blade is used, and are worth twenty-five points each. When sliced, the quote appears with the red "+25" over the "+10".

Laser Critical

These criticals appear in the Cherry Bomb Mini Game and when the Laser Blade is used. When the fruits are near the bombs, they will generate a shrouding electric arc on their outside. Quickly slice and make sure not to slice the bomb by mistake.

NOTE: Critical hits can be achieved in all modes except Zen.

_{Quotes pulled from the Fruit Ninja fandom.}