Hershel got his leg cut off
Usually when someone gets bitten by a zombie, their number is up. But over the long winter, the group came up with a plan for what to do if that happened. When Hershel is bitten, Rick wastes no time in pulling out the shiny new axe to chop off most of Hershel's leg. Though the procedure itself was pretty shocking, probably more shocking was the fact that the old guy survived it.