In Star Wars: A New Hope, when Luke finds R2-D2 who runs away to find Obi-Wan, it says something that C3-PO translates. Here is the conversation.

Luke: What's wrong with him?

C3-PO: There are several creatures approaching from the southeast.

Luke: Sand People. Or worst.

So, which worse thing was he expecting here? It should be something that is worse than Sand People, but what was it?