A 24-year-old man in the UK had his ear bitten in a row over mobile phone use on a train, British Transport Police (BTP) said.
The attack happened when the attacker complained that the victim's friend was speaking loudly on his phone on board a Southern Railway service from London Bridge to Peckham Rye.
This led to an argument during which the attacker leaned over and bit the passenger's ear.
He "eventually stopped biting the victim's ear" and returned to his seat, a BTP spokesman said.
The man suffered a deep cut to his ear and required hospital treatment following the incident at around 11.40pm on October 6.
Officers have released a CCTV image of a man they believe may have information which could help their investigation.