I have a different opinion about the wisdom of feeding hawthorn berries (haws) to
rabbits.
They are perfectly safe & beneficial for
humans & birds, but rabbits have different needs. They do not contain poisonous substances AFAIK.
However, it is a basic principal of feeding bunnies not to give them small hard seeds (eg allow them to eat fallen bird seed) or nuts with shells on, for 2 reasons.
a) Rabbits can crack a
molar tooth very easily on hard food, especially if it's unexpected - just like us.
b) Small seeds which could be swallowed whole, can form a blockage in the gut.
The normal rabbit diet is vegetation, which is extremely low in fats; so high cholesterol levels are not a problem in rabbits, & not a major predisposing cause of heart disease unlike humans.
We can all see how hard a haw is for ourselves by isolating the central seed & trying to crush it (with a knife not our teeth, or you might break one of your own teeth!
)