Re: Kind of embarrasing question...
			 
             
			
		
		
		
		IIRC the blood slaves need to be in the lab stockpile rather than the pretender to cast a ritual. 
 
 The pretender's inventory is only ever used for spells cast in actual battle. Anything cast from the strategic screen uses the lab stockpile. 
		
	
		
		
		
		
		
		
		
		
		
	
		
		
	
	
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