Final answer:
Nigel suggests that the main ingredient to Clam Chowder might be the clams' livers, according to McTeague's distracted response in the conversation.
Step-by-step explanation:
In the provided text, Nigel's comment on the main ingredient to Clam Chowder insinuates that it might be clams' livers.
When McTeague is asked and is stupefied by the commotion, he responds in a distracted manner, suggesting that the important component of the Clam Chowder may be related to the clams' livers.
It's necessary to note that in reality, clams do not have livers as we think of them in vertebrates; however, in text, the phrase 'it's their livers' indicates a belief or misunderstanding held by the character Nigel.