A local friend has the casein allergy. It sucks, cause there's a lot of baked goods and food in general she can't have. I struggle sometimes in baking becaus even butter contains it, and plant butters never quite perfectly match with real butter.
At least plant-based heavy cream works well enough. Lacks the dairy taste but it still works and whips nicely even in a cream whipper.
By this logic, a lawnmower "thinks" my fingers are grass.