Dieffenbachia plants contains oxalic acid and calcium oxalate crystals that can cause burning and swelling of the lips, tongue, and throat. It can cause difficulty speaking and swallowing (hence the 'dumb cane' common name), and nausea, vomiting, and diarrhea. The poisoning is rarely fatal to humans, but you should contact your local poison control agency if any portions of the plant are chewed or ingested.