6. Rhubarb
Rhubarb makes a fantastic pie filling, particularly in the summer, but be careful not to include its leaves by mistake. Oxalic acid, found in rhubarb, is a factor that causes kidney stones. Since it takes 11 pounds of rhubarb leaves to cause poisoning and death, it could be a long time until it has a serious impact on someone’s health. So, while you’re cooking, keep rhubarb stalks in mind.