S1·E11 The Way to Kill a Killer

When one of Nick's old friends, Mariano Montoya, comes through town on his way to sell his cattle, trouble hits in the form of deadly anthrax. The man's cattle begin to die off and it seems as though they will have to shoot them all, killing as well Mariano's dreams for the money. Until Eugene tells them of something called immunization, which he believes will work. Mariano isn't so sure however and tells them that to prove it works, the Barkleys must first try it on their own prize bull!The bull collapses and it looks as though it has been killed but then it moves and gets up, it works!! Mariano's herd is saved!