Yes, something serious is what I was saying. I am not entirely convinced that 'quick' used to mean merely alive. 'Quick' seems to be used to indicate a state of being very alive. In the past people must have been very aware of nature. They knew that roots of couch grass and hawthorne twigs could each produce whole new plants but other parts of the plant could not. They would have noticed that cutting nails to the quick was more painful then cutting a finger and concluded that this part of the body was also more vital.