Rebound
If compression controls the rate at which the shock collapses to absorb impact, rebound is the rate at which it re-extends to ready for the next blow. If you've ever ridden a sled where the rear end feels like it's trying to kick you over the handlebars, you know what too fast rebound damping can do. If the rebound is too slow, the shock will stay collapsed from one bump to the next and you are riding on a sled with an inch of travel. How do you tell? The rear end is easier to feel than the skis. If the skid kicks the back of the sled straight up as you blitz through a rough mogul section, then the rebound is too fast. If the rear end starts swapping side to side, the rebound is too slow. On the ski shocks, if the front end seems to thud through the bumps and jar your wrists, the rebound is too slow.
Very few snowmobile shocks feature rebound clickers, but if you have ones that do, remember that turning the rebound adjuster screw in slows the rebound and turning it out speeds the rebound up.