From Wikipedia:
http://en.wikipedia.org/wiki/Calcium_oxalate
"Even a small dose of calcium oxalate is enough to cause intense sensations of burning in the mouth and throat, swelling, and choking. In larger doses, however, calcium oxalate causes severe digestive upset, breathing difficulties and — if enough is consumed — convulsions, coma and death. Recovery from severe oxalate poisoning is possible, but permanent liver and kidney damage may have occurred."
I made a deal with my liver and kidneys a long time ago. We try to take care of each other for the long haul. Ergo (I really do like that word), Ergo, I avoid calcium oxalate whenever possible.