Elephants Ears are heavy feeders and like to live in rich fertile soils with good sun and water. If your elephants ear is not growing as well as you would expect, then feed it more - lots of mulch and good fertiliser or manure. 

The plant contains calcium oxalate crystals. These cause an extremely unpleasant sensation similar to needles being stuck into the mouth and tongue if they are eaten, but they are easily neutralized by thoroughly drying or cooking the plant or by steeping it in water.