Calcium oxalate is a chemical compound that forms needle-shaped crystals, known in plants as raphides

Raphides

Raphides are needle-shaped crystals of calcium oxalate as the monohydrate or calcium carbonate as aragonite, found in more than 200 families of plants.Both ends are needle-like, but raphides tend to be more blunt at one end and more tapering at the other....

. A major constituent of human kidney stones, the chemical is also found in beerstone, a scale that forms on containers used in breweries. Its chemical formula is CaC₂O₄ or Ca (COO)₂.
Quantities of calcium oxalate are found in many tropical house plants. Calcium oxalate is a poisonous substance that can produce sores and numbing on ingestion and could even be fatal.
The poison

Poison

In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....

ous plant dumb cane (Dieffenbachia

Dieffenbachia

Dieffenbachia is a genus of tropical plants in the Family Araceae noted for their patterned leaves. Members of this genus are popular as houseplants because of their tolerance for shade. The common name is "dumb cane" due to its poisoning effect on the throat due to raphides...

) contains the substance and on ingestion can prevent speech and be suffocating.