A bizarre assault investigation has been launched following reports that two men received small puncture wounds after shaking hands with an elderly woman.
Lincolnshire Police said the incident happened on August 6 on a bus heading to Skegness from Lincoln.
The two men attended hospital to have their wounds checked but were told they were not serious.
The elderly woman left the bus at Horncastle after being seen to shake hands with the men, the force said.
Officers have appealed for any witnesses to come forward and have released images of four people they believe may have seen what happened.
A spokesman for Lincolnshire Police said: “We would like to make clear that the people in these photographs are not being treated as suspects, but we would like to speak to them as they may have information relating to this incident.”