Luke almost murdered Clementine! Think about it, Luke threw Clementine on the floor making it look like he just panicked over the bite while actually trying to give her a concussion. Luke then devised a plan on putting Clementine in the shed while looking like the good guy while knowing that if she would've slept in the shed with that concussion, she would've went into a coma and died(no one would have suspected him since he looked like he was protecting Clementine)! Which would have made Luke appear to be right about the bite. Also Luke throwing Clementine on the floor could have given Clementine a blood clot which would've blocked off the blood supply to a large part of her brain and would have died while still making it look like the bite is what killed her. Luke knew this and attempted to murder Clementine by dropping Clementine on the floor so the group wouldn't have to deal with her but was unsuccessful. I knew he seemed suspicious and untrustworthy for a reason. The nice guy charade is just a ploy until he can organize a new scheme towards taking out Clementine inadvertently.