Several characters have talked about Glenn Rhee since he died on The Walking Dead. In fact, both Glenn and Abraham Ford have seen a few tributes throughout Season 7.
For Negan to make a reference to Glenn through some subtle dialogue callbacks is quite ironic, though, seeing as he is the man who bashed skulls in the Season 7 premiere. Until now, most fans did not catch the Easter Egg line of dialogue which Negan delivered to Carl in Episode 7x07 (Sing Me A Song).
In Season 3 Episode 16, Welcome to the Tombs, Rick talks to Glenn about Carl, saying, "He's still a kid. It's easy to forget that sometimes."
In Episode 7x07, Negan is speaking directly to Carl, saying, "It's easy to forget that you're just a kid."
Of course, Season 3 contained some of the most growth for Carl. It was the time when he had to put his mother down and the rest of the characters insisted on seeing him as a child. Glenn was always a pillar for Rick and others to lean on as he would put others before himself and Negan took that away from the group.
This is hardly the first time dialogue has mirrored previous seasons of The Walking Dead. Episode 7x03 took a moment from Episode 3x07 and referenced it in dialogue. During Daryl's imprisonment in Negan's Sanctuary, Negan told Daryl, "You don't scare easy." This is a direct reference to Merle's dialogue while Glenn was taken prisoner at the Governor's Woodbury community.
The Episode 7x03 and 7x03 mirroring sounds like too much of a coincidence to not have happened on purpose. So, in the spirit of Walking Dead writer conspiracies, 3x16=48 and 7x7=49. Intentional? Significant? Probably not but conspiracies are still fun and Glenn is still dead, either way.
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