I started rooting for the Abbies last week. After this episode's flashback, I wonder if the show wants us to root for them. Or at least hope they don't get wiped out. The Abbies seemed very peaceful just a few years ago, which I guess is consistent with them evolving to their current state from humans in just 2,000…

"Walker told me I have AIDS."

A phase inverter. An equal but opposite signal is the audio equivalent of an evil twin.