The Hundred-Acre Wood suffered a famine that resulted in Pooh and Piglet eating Eeyore alive as they relied on Christopher Robin to provide food for them. It would be one thing if they were remorseless about their actions and immediately became sociopaths after the act, but they do not. They temporarily snap back to their senses and realize the horror they've committed and it traumatizes them so much that they make a vow to never speak again.
The animated opening reveals that Winnie the Pooh and his friends were always real, rather than imaginary friends created from stuffed animals. As a child, Christopher Robin stumbled across a strange group of creatures while exploring the Hundred-Acre Wood, and while they apparently weren't hostile then, the narrator refers to them as "crossbreeds" and "abominations". It's never revealed exactly what they are and where they came from.
The death sticks out even further because of the sheer cruelty of it. Most of the other kills were made with whatever was on hand and relatively quickly. The logical choice for Pooh and Piglet would have been to drown Lara in the hot tub where they find her (which would also run less risk of alerting the others). Instead, they drag her to the dirt road and wait for her to regain consciousness before they crush her skull. The brief Slasher Smile Pooh shows just as he starts driving, and Piglet's laugh at Lara's death, shows that this was a kill they wanted to savor.
