The cells of the plant contain needle-shaped calcium oxalate crystals. If a leaf is chewed, these crystals cause a burning sensation in the mouth and throat; swelling can occur along with a temporary inability to speak, and from this effect the plants are also called dumb cane. Chewing could result in death if the swelling blocks the airway. Slaves were sometimes punished by having dieffenbachia put into their mouths.
If you have this plant in your house or yard, wash your hands after handling it.