Anybody think that the horn sounding was a way to thin out the herd? All the volunteers are outside, leaving only the weaker ones at Alexandria, with the exception of the ones from Rick's group that can take care of themselves. Rick seems to be wanting to test folks and make them fight. This could be a way to do that. The ones that step up survive, the ones that don't, well, Rick doesn't want them anyway.
I'm kind of surprised that Ethan Embry's character didn't last longer. It could have been pretty interesting watching him change.