Final answer:
An open wound caused by a sharp object is described as an incision, and cutting into the papillary dermis layer of skin is necessary for bleeding to occur.
Step-by-step explanation:
An open wound caused by a sharp object is best described as an incision. An incision is a clean cut through the skin or other tissue made by a sharp instrument, leading to a wound with smooth edges. In the case of a small amount of blood noticed after cutting oneself with a sharp knife, the individual likely has cut into the papillary dermis, one of the deeper layers of skin that contains blood vessels. If just the topmost layer, the stratum corneum, were cut, there typically wouldn't be bleeding since it consists of dead skin cells and lacks blood vessels.
The other options provided describe different types of wounds: Avulsion refers to a wound where tissue is forcibly detached, contusion denotes a bruise caused by blunt trauma that damages blood vessels under the skin, and abrasion is a wound caused by scraping off a layer of the skin.