The teeth of rabbits grow throughout their lives, up to 10 centimeters a year. Therefore, they must be worn down regularly, otherwise there is a risk of abscesses and starvation. The most suitable for this purpose are things that contain a lot of raw fiber and other hard elements. As a rule of thumb for herbs and leafy greens, the darker the green, the better for tooth wear. It’s also quite possible that’s what’s behind eating rhubarb.
I’m not sure there needs to be much short-term adaptation involved… as I said, in small amounts it’s not too concerning, as with many other plant substances and toxins.