Police have launched an investigation Friday to nab a suspect who secretly stuck a needle into a chair in a study room in Seoul, resulting in injury to the next user of the seat.

According to local reports, the victim was stabbed by a sewing needle hidden under the cushion when they sat down at a reading room in Shinlim-dong, Gwanak-gu, on Jan. 2. The victim suffered a minor thigh injury.

The reading room is mainly used by college students preparing for the civil service exam.

“Assault charges will be applied to the perpetrator and we are investigating whether there have been similar cases,” a Seoul Gwanak Police Station official said.