A pathologist told a court he did not believe stab wounds were inflicted by accident during a struggle between two love rivals.
Spurned husband Paul England, 38, is alleged to have attacked Marten Moore with a dagger after England's wife Julia left him and moved into Mr Moore's home.
England is alleged to have worn his wedding suit when he kicked down the door to Mr Moore's flat in Bishopric Court, Horsham, on January 24 this year, when the couple were in bed.
While his wife fled naked for help, England is accused of inflicting potentially life-threatening wounds to Mr Moore's chest and abdomen with the seven-inch blade.
He then slashed his own wrist with the Commando-style weapon.
England, of Bedford Road, Horsham, has denied attempting to murder Mr Moore, 35, a bank worker.
The jury at Lewes Crown Court has heard how he told police Mr Moore was hurt by accident when he ran on to the knife he was holding.
Home Office forensic pathologist Dr David Rouse told the jury the weapon was very sharp and it would only take moderate force to inflict the wounds.
He said: "You would expect a much larger wound and much greater internal damage if he had run on to the knife."
England also denies wounding with intent to cause Mr Moore grievous bodily harm and aggravated burglary with intent to inflict grievous bodily harm on his former wife.
The trial continues.
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