Final answer:
The unusual feature of a black dog would logically refer to an atypical anatomical trait, such as having an abnormal number of toes on its paws; however, normally dogs have four functional toes and sometimes an additional dewclaw.
Step-by-step explanation:
The question relates to the anatomical features of a black dog which is a biological subject. Without greater context, it is difficult to know exactly what is meant by 'most unusual feature.' Assuming the question refers to a typical trait that would be considered unusual for a dog, none of the options provided (1) One finger from one hand, 2) Two fingers from two hands, 3) Two fingers from one hand) are characteristic of a canine. Dogs normally have four functional toes on their paws and sometimes a dewclaw, which can look like a fifth toe; this dewclaw can occur on either the front or back paws, depending on the breed. An unusual feature in this context would be outside the norm of this typical paw structure.
If the question is asking specifically about an unusual genetic mutation or condition that would result in a black dog having fewer toes, then the most unusual feature would be a deviation from the expected number of toes, such as only having two toes on a paw. However, this would be an extremely rare condition and not typical of black dogs as a whole.