Chicken immunity is level 10 of the chicken title (alektorophobia). It'll come naturally after a few lives, or you can force it by rushing to day 31 and dying a few times.
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Thanks for reply. Looks like I pretty much reached the end of current version then. I had like three dozen 'rewinds', multiple times doing all dungeons, usually reaching about level 62-73, got pretty close to the final form of most title evolutions, and poisoned myself to death constantly to get the perfect immunity, gaining immunity to the succubus mind control too, and getting chicken immunity. Looking forward to how these titles may benefit us later in story, like at a banquet.
As a sidenote: I think there's a bug with the RL programmer title. I used dungeons to level up this title to seven or eight, but every time the character is reborn the initial list of titles only shows it at the top of list, at the base 1st level, even though the parents later do remark about the unknown title in strange language.