In every section of the mural, the people are fighting each other and not the walkers surrounding them.
The walker that Dog (aka Seven) takes down during the fight sequence in the tunnel was actually one of his trainers.
Maggie's "SOS" message from under the train car is the first time a character on the show has communicated using Morse Code. Executive Producer Denise Huth says it's possible she learned it from the Morse Code Chart that was on the wall at Rick and Michonne's house.
Viewers may have noticed that two of the advertisements inside the train cars were actually Easter eggs from the show. One was "Duane Jones Whiskey" which Father Gabriel and Aaron stole from Mays last season, and the other was "Gorbelli Foods Company" which Tara's dad worked for pre-apocalypse.
The mural Daryl finds was inspired by two works of art: The Triumph of Death by Peter Bruegel the Elder and The Garden of Earthly Delights by Hieronymus Bosch.