The flipper of a fish spatula should be thin and flexible, so that it slips smoothly under even delicate items and is easy to maneuver around a crowded pan. If it's too stiff, it can be hard to move the short handle (and your knuckles) away from the hot edge of the pan, or to slide the blade under a fillet at an angle that won't disturb its neighbor. Wide slots in the flipper help with flexibility, and also allow oil to drain off quickly. But the spatula shouldn't be too flexible: It still needs to be sturdy enough to lift a big burger or steak without buckling or sagging. The last thing you want is your food sliding off it onto the floor.