He’d sawed off his leg to escape the zombies.  Fortunately, he still had his trusty chainsaw.

He locked himself inside an empty store and stopped to rest.

Suddenly, he felt a sharp pain in his left arm: an infected scratch.

Survival ended up costing him an arm and a leg.

When the zombies appeared, he found his calling, shredding down the legions of the dead.

Surrounded, he had to cut his way into a shed to hide.  Then a zombie bit his leg.  Got to saw it off, or become a zombie.

Easier shed than bone.