How can you tell when it's time to feed your corn snake larger mice?

The pet store said that before my corn snake moves up to bigger mice it will eat several pinkies. Well, I just fed Tiberius two pinkies, and when I put him back in his cage he was shaking his tail and sticking out his tongue (which I know is him sniffing)... Would this be him looking for more food? Or was he just grumpy that I picked him up to put him back? Thanks.