We know that domestic cats use their whiskers to judge whether or not they'll fit in certain places. Turns out their bigger cousins do something pretty cool with their own whiskers.
Tigers have nerve endings at the base of their whiskers that let them detect distances and changes in their surroundings. They also do something pretty cool when they hunt: The whiskers encircle the prey's neck and they can detect if they have a pulse. That's how they know to stop attacking.