A bizarre assault investigation has been launched following reports that twomen received small puncture wounds after shaking hands with an elderly woman.
Police say the incident happened on a bus heading from Lincoln to Skegness on 6 August.
The two men suffered small wounds on their hands and later attended hospital but were told their injuries were not serious.
The woman left the bus at Horncastle after being seen to shake hands with the men.
Officers have appealed for any witnesses to come forward and have released images of four people they want to speak to, who may have seen what happened.
"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."