1

They are sick, wounded, or otherwise in distress.

2

Tensions are running high. They may panic and/or become violent if provoked.

3

They mistake the player characters for someone else, or misunderstand their intentions.

4

They disappear after the encounter.

5

They have an important item.

6

They have a hidden stash of valuables.

7

One of them tells a story, plays a song, reads poetry, preaches, etc.

8

They are arguing or brawling with each other.

9

They don't speak a common language.

10

The player characters have met them before.

11

They are working for an enemy (willingly or otherwise).

12

They cause a hazard, injury, or setback for the player characters (intentionally or otherwise).

13

They have the same quest/goal as the player characters.

14

They know or discover another character's secret.

15

They are unexpectedly friendly or unfriendly toward the player characters.

16

They are drunk (etc) and acting unusual.

17

They are in disguise or otherwise not what they seem.

18

They have something in common with a player character.

19

They have a problem or job that they would be willing to hire the player characters to handle.

20

They have extra protection (guards, wards, traps, etc).