Growing up in a small town in the Midwest, we neighbor kids were quite familiar with the odd celery-like stalk with an enormous leaf at the end of it. Rhubarb lined one side of a neighbor’s house like decorative landscaping. We’d break off a shaft of it and dip it in a cup of sugar with each bite to soften the sour. In the days before calling 911 over unsupervised children, the adults simply shouted over their shoulders, “OK, dear, just don’t eat the leaves; they’re poisonous.” That seemed to be sufficient warning. But are they really? Oxalic acid, which occurs in many vegetables, fruits, and even cocoa, is the offending culprit. It’s also found in the rhubarb stalk, but it’s the higher concentrations in the leaves that prompt the warning. Too much can enter the toxic zone, giving one a bellyache or in worse cases, vomiting or diarrhea. Farther …