What does the phrase "taken with a barrel of salt" mean at end of the second paragraph

A．studied sleepwalking for at least ten years
B．concluded that sleepwalkers are partially asleep in their sensory area
C．maintained that it is a mistaken belief that sleepwalkers are immune to injury
D．A and B

A．It is caused by emotional conflict or guilty conscience.
B．It is the acting out of a vivid dream.
C．Somnambulists are asleep during their sleepwalking.
D．It is dangerous to waken a sleepwalker.