Nick's most likely suffering from a fungal infection in his nail. It is possible that this condition is onychomycosis.
No, this does not cause any severe problems, despite the unsettling sound. The "crack" you hear is simply the joints releasing built-up gas. It is not bad for your health.
Answer:
the infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host.
I don't see any answer choices but
Health is a dynamic state of wellbeing characterized by a physical, mental , and social potential that meets the demands of a life commensurate with age, culture , and personal responsibility.