Well, after Rick killed Shane, Shane turned into a zombie. Usually, you don't turn into a zombie unless you're bitten or infected by another zombie. So Rick realized that they all are probably infected and will all turn into a zombie, if they die.
ahh.. I see. from watching zombie movies, thought you had to be bitten to turn zombie so I
was confused why Shane turned into one.
Well, hopefully I'm able to watch it this Sunday but sux cus football is on too!