result is a gross underestimate. Twenty of the quills 

 in my glove take more pull than the balance can reg- 

 ister. In a later experiment I discover the extraction 

 tension for individual, well-rooted quills can be 

 twenty-five times higher than my first calculation 

 suggests, or in excess often pounds apiece! 



Even if the extraction force were "only" 6.7 

 ounces per quill, extracting all eighty-four quills at 

 once would take a pull of more than thirty-five 

 pounds. That is well above Loretta's body weight — 

 thirteen pounds — and far more force than she could 

 conceivably exert on her own, especially consider- 

 ing that porcupines have relatively little muscle com- 

 pared with other mammals. 



So how did Loretta separate herself from the 

 glove? Not by pulling her quills out of it. Instead, 

 she shed them from her skin. Does that solve the 

 paradox? It might if eighty-four quills could be re- 

 moved from Loretta's skin with a force roughly 

 equal to her weight — about two and a half ounces 

 per quill. I do the obvious experiment. I anesthetize 

 Loretta and seven other porcupines with a quick- 

 acting drug, and measure the withdrawal tension 

 of a few of the animals' quills. The average quill- 

 withdrawal tension is 3.2 ounces per quill, still too 

 much for a little animal to disengage quickly from 

 her target. In other words, when Loretta struck my 

 glove, she should have remained stuck to it, tied 



March 2006 NATURAL 



