expendable - Not essential, able to be used up or sacrificed without significant loss, easily replaced or not necessary for long-term use.

The workers didn't feel any sense of job security, and they felt expendable, because they were fired whenever the demand for the factory work slowed down.
slug - A tough-skinned terrestrial mollusk that typically lacks a shell and secretes a film of mucus for protection. It can be a serious plant pes

A slug is one of the slowest-moving animals on earth, so someone who is afraid of them can easily run away.