What are the signs of a corpse?

What are the telltale signs that indicate the presence of a corpse? Are there any visual cues, such as discoloration or rigor mortis, that can be easily recognized? Are there any specific smells that may accompany a deceased body? Are there any behaviors or actions that individuals might exhibit upon discovering a corpse, such as shock or revulsion? Additionally, what steps should be taken if one suspects the presence of a corpse, and who should be contacted in such a situation?