omg - you know the guy who was having the firestar headaches
if you make him your mate and give him deathberries that aren't hidden, HE TAKES THEM
Viewing post in West Woods: Over Borders comments
This is because you're a full medicine cat (if you didn't cheat and just kill off the cats guarding the Cold Stone immediately.) The cats trust you with what herbs you give them, but the game is coded so that the cat won't die if you give them deathberries that aren't hidden. This is with literally every cat in the game, so this information isn't actually new.