This can be an example of nostalgia. (Nostalgia is a sentimental longing or wistful affection for the past, typically for a period or place with happy personal associations according to Oxford Dictionaries)
The answer is B) It suggest a tone of worry. The reason is because the phrase "knitting their cheeks" means the that the llamas were moving their jaws. This along with the fact that they were contemplating the writer suggests that the llamas are unsure of the writer.
