When he boarded a train on the North-South Line at Woodlands MRT station at about 6.45pm, the last thing he expected was to see a man strip.
But that is what student Ang Guan Wei, 22, and other commuters on the train saw on Thursday.
Mr Ang, who was headed towards Marina Bay for dinner, told The New Paper that he was watching a video on his phone when the man threw a plastic bag on the ground near him.
"I thought that someone had dropped the plastic bag, so I looked up, and I saw the man pacing around the cabin," said Mr Ang, who was standing on a cabin connector.
At first, no one was interested in what he was doing. But as the train passed Admiralty MRT station, the man started to take off his clothes, he said.
"He walked around for a while, then suddenly stripped (himself) naked," said Mr Ang.
He said most commuters were disgusted and some began to move out of the cabin.
But there was no commotion and no one questioned the man about his actions.
Throughout the entire episode, the man remained "completely silent", said Mr Ang.
In his naked state, he then tried to approach other commuters in the same cabin. After performing a sex act, the man lay down in front of the train door when the train pulled into Sembawang MRT station. By then, most of the passengers had moved to other cabins.
A female passenger in the same cabin pressed the Emergency Communication Button.
When the train arrived at Khatib station, SMRT officers boarded it and escorted the naked man out.
An SMRT spokesman confirmed that staff had boarded the train at Khatib station at 6.56pm. The man was handed over to the police, the spokesman said.
The police said they got a call at about 7.05pm asking for help. They arrested a 32-year-old man at the station for committing an obscene act. They are investigating.
Anyone found guilty of indecent behaviour in a public place can be fined up to $1,000 or jailed for up to a month.
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