A lawyer defending a man accused of murdering his daughter during a row over a cigarette lighter says his client did not know he stabbed her in the chest but "these things sometimes happen".

Kelvin Clive Hart, 45, is on trial in the West Australian Supreme Court charged with murdering Ricki-Lee Hart, aged in her 20s, in December 2012.

Defence lawyer Tom Percy said in his opening address on Monday that it was "a most unusual case" and insisted his client did not wilfully cause the knife to enter her body.

"These things sometimes happen," he said.

Mr Percy said there was no indication at the time that Ms Hart had been stabbed and she might not have known about it until she collapsed because there was very little blood.