Which one is correct and why?
the sloth hangs from trees by its long rubbery
limbs, sleeping 15 hours a day and moving so
infrequently
OR
the sloth hangs from trees by its long rubbery
limbs, sleeps 15 hours a day, and it moves
infrequently enough
The former is correct. Of course the first letter needs to be capitalized. And it needs a period. The latter is incorrect for those reasons among others. If you omitted “it,” it would be correct. Alternatively, you could insert “and” between “limbs” and “sleeps” and omit the comma. Coordinating conjunctions should combine like things. Here it attempts to combine verbs of the same subject and an independent clause at the same time.