the snails are very quick to eat anything that is dead, so I am sure the shrimp was either already dead or very close to dead before the snail started eating it. 
 
I have 7 large Nassarius snails in my 33 gal and they have never harmed anything, other than stealing food from polyps. 
		
	
		
		
		
		
		
	
		
		
	
	
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