Ask Mr. Smarty Plants

The ASPCA (American Society for the Prevention of Cruelty to Animals) has an excellent website that lists plants that are toxic or non-toxic to pets. Since castor beans (Ricinus communis) are not native plants (but they have naturalized in many places in the South), Mr. Smarty Plants can't advise on this. So looking at the ASPCA page for castor beans shows that the seeds are very toxic to dogs, cats and horses. 

Here's what the ASPCA information says about castor beans ... Beans are very toxic: oral irritation, burning of mouth and throat, increase in thirst, vomiting, diarrhea, kidney failure, convulsions. Access to ornamental plants or pruned foliage most common in poisonings. Ricin is a highly toxic component that inhibits protein synthesis; ingestion of as little as one ounce of seeds can be lethal. Signs typically develop 12 to 48 hours after ingestion, and include loss of appetite, excessive thirst, weakness, colic, trembling, sweating, loss of coordination, difficulty breathing, progressive central nervous system depression, and fever. As syndrome progresses, bloody diarrhea may occur, and convulsions and coma can precede death.

In addition, the Veterinary Medicine Library indicates that all parts of the castor bean are toxic, but the seeds are the worst.

The Veterinary Medicine Library web page on castor beans says, "All parts of the plants are toxic, but most dangerous are the seeds. The most susceptible animal species include cattle, horses, sheep, pigs, fowl, rabbits and other small animals. Seeds ingested at 0.2% of body weight have caused toxicosis in cattle and 0.01% of body weight was toxic to horses."

.