"Maybe it was a lapse in concentration - it just happened so quick. When I looked down I thought, 'They shouldn't be lying there'."
His thumb and finger fell to the bed of the splitter.
The postie, who happened to be there, called emergency services after the November 30 accident.
Mr Mulholland, who is right-handed, said he felt no pain at first and there was surprisingly little blood.
His neighbour picked up the severed thumb and finger and, on instructions from the ambulance call centre, put them in a wet cloth inside a plastic bag. The package was placed on ice in a chillybin brought by a nurse and doctor.
The chillybin and Mr Mulholland were taken to Middlemore Hospital, where he had operations, headed by plastic and reconstructive surgeon Stanley Loo, to re-attach and repair the thumb and finger.
The digits were on ice for about four hours before he went into surgery.
"My biggest thing is I have got Stanley to thank because everybody else thought they [the finger and thumb] were goners," Mr Mulholland said.
"The first thing Stanley said when he saw me was, 'We'll put those back on'. That's amazing."
In the first, 10-hour operation, four surgeons reconnected bones, then tendons and arteries and veins.
The following morning the blood flow in the thumb was poor, necessitating a further four hours in the operating theatre.
Now, more than three weeks after the surgery, Mr Mulholland is recovering at home.
"It's going really well. Stanley is really pleased with the progress. Everything has been textbook."
Mr Mulholland's hand is still bandaged and he has to be careful to keep it warm to promote good blood-flow.
"There's a slight bit of feeling. [Mr Loo] said he wasn't expecting me to have any feeling that quick."
Mr Loo said the aim was to give Mr Mulholland back a functioning thumb and index finger so he could care for his wife, who has Alzheimers.
He would have up to six months of physiotherapy and should eventually be able to fully extend the re-attached finger and thumb.
They would probably regain 80 to 90 per cent of normal function.