A poisonous snake
It wasn’t until Lily mentioned the snake that they realized they needed to do a blood transfusion to save his life. They arrived barely in time. Because if the venom had spread any farther, there would have been a funeral rather than a celebration…
The end
They didn’t want to stay near venomous snakes or in the area where John almost died. So, as soon as John recovered completely, he and his family decided to relocate. They relocated to a peaceful street in another state, where there would be no dangerous snakes. The end, or so they hoped.