Final answer:
Muttered means to speak in a low voice, indicating Jess's annoyance or reluctance, without wanting to draw much attention.
Step-by-step explanation:
The most likely meaning of "muttered" in the sentence is that Jess spoke in a low voice, almost under his breath, typically because he was annoyed or displeased. The word indicates that the character did not speak loudly or clearly but murmured something softly enough so that it may not have been fully audible or coherent to others present. This form of speaking is often used to convey reluctance or discontent without drawing too much attention to oneself.