While the stalks of rhubarb are edible, the leaves are toxic to both humans and animals. They contain high levels of oxalic acid, which can cause kidney failure, seizures, and even death if ingested in large quantities. It is important to remove and discard the leaves before cooking or eating the stalks. Additionally, it is recommended to avoid consuming large quantities of rhubarb stalks in one sitting, as they can also contain high amounts of oxalic acid.