The Walking Dead released its Season 9 trailer during its panel at San Diego Comic-Con, a big day where Andrew Lincoln confirmed that he's leaving the show and it was revealed that the Whisperers are coming and Samantha Morton will play their leader Alpha.

The Whisperers are adversaries from the comics who skin walkers and wear the dead epidermis as their own, and live among the dead undetected. Their name comes from how they communicate. Their arrival was biggest news to come out of the panel (we already knew Andy was leaving), but other than the casting announcement it seemed like the Whisperers were being downplayed a little bit. The trailer focuses on Rick Grimes (Lincoln) trying to keep the communities together among mounting tension within the group and at first glance barely hints at the Whisperers at all. But sharp-eared fans on Reddit with comics knowledge noticed something.

There's a scene at the end of the trailer where Rosita (Christian Serratos) and an unidentifiable male character are hiding in mud from a horde of walkers passing by. They are terrified in a way of these tough characters almost never are, even in the face of a big horde. I'm not a comics reader, so when I first saw it, I assumed it was a hint that the Whisperers were among the horde. But comics readers knew that there should be a line of dialogue in that scene that would explain why they're so scared. So they listened over and over again until they heard it.

Listen closely to the walker growls. I admit I didn't hear it until like the fifth time I watched it.

"Where are they?" from r/thewalkingdead

HOLY S---! The Whisperers are in the trailer, and they aren't whispering, they're communicating through walker growls! They're Growlers, a term for the dead that was actually used once in Season 6 by a small group of Saviors who captured Carol (Melissa McBride) and Maggie (Lauren Cohan).

In the comics, this iconic scene is the cover of issue #130 and is the introduction to the Whisperers. It happens with two characters who don't exist on the show (yet?), Marco and Ken. They hear "where they go?" and think the dead have learned to speak. Which seems to be what's happening here, since that would horrify even a character as courageous as Rosita.

The Walking Dead Season 9 premieres Sunday, Oct. 7 at 9/8c on AMC.