Chp 48 of Less Wrong's HP fanfiction:
Harry Potter & The Methods of Rationality.[link]
HarryPotter & TerryBoot.
Harry making theories during breakfast about sentient/self-awareness possibility of snakes & other animals caused by spell that enable us to talk to animals(like parselmouth to snake or poultrymoth to cows?) which make him avoid eating meat for the time being.
Unfortunately he realized that if such spell to talk to animals exists, there's the possibility that there is a spell to talk to plants, giving plants self-awareness(becoming sentient)