That looks like a nice example.  From what I have heard, it is very rare to find the by-knife, as they are considered more important to the owners due to their being used to clean & prepare the taken heads (rather than just take them). 
 
I have to admit that there is something very creepy to me about mandaus.  It can't be just the head-hunting thing.  Maybe it is the decoration of the carving.
		 
		
		
		
		
		
		
		
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