Poison Mushroom Cookie was wandering around the woods, collecting mushrooms and whatnot... Whatever it is, they do, when they heard something, they didn't fully proccess what it was at first, but then they realized they were hearing crying... That ushally isn't good.

they followed the noise, and noitced another cookie, around the same age as them... ooo a new friend...

"Hi... why are you crying...?"

they approached the cookie, before holding up a mushroom he had collected...

"Don't cry... have a shroomie..."

...he attempted to give the most likely very poisonous mushroom to the crying cookie.