Mullet, appreciate the happy faces from an expert knapper like yourself. One more thought on the nipple and I'll shut up and let more knowledgeable people comment. When working the nipple one must always keep in mind that each nipple has its own unique characteristics. Some require only gentle manipulation before they become properly extended, while others require a more aggressive approach. Whichever the case, each must be massaged properly to achieve its maximum extension and firmness. When this is accomplished a satisfactory piece can then be knocked off.