 While his group escapes from the Center of Disease Control and Prevention , Jenner whispers to Rick about the virus that has caused the zombie apocalypse . Initially there was no indication as to what Jenner said to him ; the dialogue was previously inserted into the episode 's script but was later removed . " I 'm so pleased they didn 't reveal it , " said Andrew Lincoln , " because it was scripted , and extremely powerful , and I said to everyone , ' Burn this page : No one should know apart from Rick and Frank . ' It 's brilliant that they left it [ as a mystery ] — it 's perfect , it 's so classy . " Kirkman was content with the idea of teasing Jenner 's revelation in lieu of blatantly revealing anything about the origins of the virus . " I thought it was a great addition . I 'm very much opposed to showing what the actual cause [ for the zombies ] is and explaining how things work , but teasing a little bit is a great thing . If it adds an extra layer to the drama , then I 'm all for it , " he stated . " It also led up to the fantastic mystery of the whisper Jenner gives to Rick at the end of that scene . That 's going to play into Season 2 quite a bit . I know where that 's going and it 's really a cool bit . " It is not until the second season finale , " Beside the Dying Fire " , that Rick reveals Jenner 's message to the group . 
