If you're part of the crowd that thought Season 2 was too slow, you should love Shane! If he even suspects there are infected nearby, you can absolutely bet he'll be determined to slaughter them. The walkers were safely contained in the barn for God knows how long, but Shane couldn't resist the urge to slaughter the trapped group of zombies. Next time you think of sipping that haterade and complaining about Mr. Walsh, just realize Shane is trying to make things entertaining for you one shotgun blast at a time.