Cashiering

I ask all you nerds with nothing else to do to comment on this situation--I'm finishing a transaction with Customer #1. Customer #2 comes into view with something in his hand to purchase and cust #1 waves him over to her, effectively motioning him to cut in line in front of other customers who are patiently waiting and putting their purchases on the conveyor belt. Should I ring up cust #2 or should I ask him to take his place at the end of the line? What would you do?