People had lots to say about chollas. These cacti propagate by growing nodular branches that break off when a passing animal gets snagged on their thorns. Dr. Hellman had apparantly presented their dangers to his students all too vividly. It often seemed as if they would rather throw themselves onto a bed of prickly pear than chance an encounter with a cholla, and shouts of, "Cholla!" rose up like battle cries wherever we hiked.
So, we were amused when Kelly and Sarah emerged from their separate tents one morning dressed not only identically, but in the color of the cholla. People were referring to them as the "Cholla Chicks." We'll have to see if it sticks (so to speak).