Jurors have watched shocking video of a "quick and frenzied" fatal attack on a train passenger.
IT consultant Lee Pomeroy, 51, was stabbed 18 times, the Old Bailey was told.
Jurors sat in silence as they were shown graphic video of the incident on a Guildford to London train on January 4.
Pencille looked straight ahead in the dock, avoiding screens set up to show the footage.
Prosecutor Jake Hallam QC said: "The incident lasted 25 seconds and during those 25 seconds Mr Pomeroy sustained 18 stab injuries."
British Transport Police Detective Constable Marc Farmer replied: "Yes, that's correct. It was a quick and frenzied attack."
Jurors saw images showing Mr Pomeroy and his 14-year-old son arriving at London Road station in Guildford and collecting their tickets before heading to platform two.
Shortly afterwards, Pencille was dropped off by his girlfriend Chelsea Mitchell and boarded the 1.01pm train to Waterloo.
He walked back down the carriage as Mr Pomeroy and his son were coming the other way.
It is claimed a row began over blocking the aisle and quickly escalated.
Mr Pomeroy was shown getting up and following Pencille into the next carriage and stood with his hands in his pockets during the argument.
The defendant appeared to gesture with his hands and make a call, allegedly to his girlfriend, to say: "I'm going to kill this man. He'll be dead."
Pencille, who has admitted possessing a knife, appeared to strike out at Mr Pomeroy's neck then continue to stab him as Mr Pomeroy attempted to defend himself.
Afterwards, Pencille is seen in the footage to bend down and pick up his sunglasses and mobile phone before leaving the train. Jurors have heard how he was picked up at Clandon station by 27-year-old Mitchell and taken to her home.
Pencille, of no fixed address, has denied murder, and Mitchell, of Farnham, Surrey, has pleaded not guilty to assisting an offender.