Final answer:
To bleed from a cut, the individual must have penetrated the dermis layer of the skin which contains the majority of blood vessels.
Step-by-step explanation:
If an individual notices a small amount of blood from a cut caused by a sharp knife, it indicates that the skin layers were penetrated deep enough to reach the blood vessels. Specifically, the layer that must have been cut into is the dermis, the second layer of skin beneath the epidermis. The dermis houses most of the skin's blood vessels, so when this layer is breached, bleeding occurs.