The humans show the dear technician that this particular acid is completely harmless to their kind, by slicing one of the fruit into a thin slice, and eating it raw. Of course, the human that did so was an oddball, they actually LIKED eating lemons the way people ate oranges. But then again, they liked grapefruit, too!
Roark stared. She was still counting the seconds long after the Human who drank the acid should have foamed at the mouth and passed out. Yet there they were, still standing, still breathing, still alive. She couldn't believe that they were still alive.
The Humans stood and stared at Roark for a terrifyingly long time. "OH," they chorused. "The citric acid."
The one who had been bare-handed mashing the cleanserfruits for their juices started peeling one. Also bare-handed. The rest of the Humans started reacting with disgust.