The scenes of Negan's (Jeffrey Dean Morgan) compound were filmed at a decommissioned telecommunications facility. It was allegedly bought by a private investor who used it to search for extraterrestrial life.
Carol is seen writing in her notebook how many humans she has killed. It reads: "R - K,D - L - Terminus/Courtyard 3? - CandleWoman 4 - Ws 7," totaling to 18 which she circles. These notes are presumably referring to Ryan Samuels in Infected (2013), Karen and David who she scorched in the same episode, Lizzie Samuels in The Grove (2014), multiple Termites of Terminus when blowing the propane tank in No Sanctuary (2014), the Candle Woman, Mary, who she shoots and leaves to be consumed by Walkers in the same episode, and multiple Wolves who attacked Alexandria in JSS (2015).
Greg Nicotero said that he used Johnny Depp's head for the scene of the three heads. The other one was Greg's head.
Rick's (Andrew Lincoln) use of the words, "We have to come for them before they come for us," is the exact same thing he said in episode 6.1, First Time Again (2015), when they were leading the walkers in the quarry away from Alexandria.
This is the first episode where you hear The Saviors infamous whistle.