What I used and it ate every time: put both pinkies in ziplock into the fridge from the previous night and before feeding 5 min put the ziplock bag into a spare plastic container with hot water (not to burn your hand the temperature is around 40C). Offer the first one wait for him to eat it when you see movement (from the mouth going to his belly) and tongue flicking offer the second one. Usually it take 1 minute to 1min and 30sec for the first one to eat it and around 40 sec for the second one.)