One type of endocytosis, phagocytosis, or cell eating, occurs when receptors on the cell's surface encounter a particle to be ingested. The cell then extends a projection called a pseudopod. In mammals, the object is often an invading microorganism or cellular debris from damaged tissue. The pseudopod surrounds the item, and the membranes fuse together creating a vacuole with the particle trapped inside. Eventually, the vacuole fuses again, this time with a lysosome which is full of enzymes ready to digest the invading particle.