Ever wondered why your teeth feel furry after eating spinach?! Well this is due to the high oxalic acid content of spinach. The oxalate in the spinach leaks out during chewing, bonding to the calcium in our teeth. The formation of these crystals causes a gritty feeling.
Other foods high in oxalic acid include rhubarb, beetroot, kale and chocolate. Boiling or cooking food will reduce the oxalic acid content and thus the furry feeling!