When you take the Search action, you make a Wisdom check to discern something that isn't obvious. The Search table suggests which skills are applicable when you take this action, depending on what you're trying to detect.
Table: Search
| Skill | Thing to Detect |
|---|---|
| Insight | Creature's state of mind |
| Medicine | Creature's ailment or cause of death |
| Perception | Concealed creature or object |
| Survival | Tracks or food |