Could something have been sprayed?
The birds were among hundreds lined up in their cages ready to be judged Gwynedd Budgerigar Society Open Show in North Wales when disaster struck.
One toppled off his perch then others began "dropping like dominoes", according to the organizers.
Owners fearing a gas leak – canaries have highly sensitive respiratory systems and were once used down mines to detect leaks – grabbed their cages and ran for the door.
Some of the birds, which are worth around £1,000 each – were revived outside but in total 38 died.
"After five or ten minutes as many as 12 had died. I lost one bird myself," organiser Rob Hughes said.
"We saved the majority but what happened was utterly horrible. It was a freak event. We may never know the exact cause."
Retired pet shop boss Dave Cottrell, 55, lost ten birds at the event, at the end of last month.
"They were dying by the second," he said. "The odd thing is, I have asthma but I was unaware of anything."
Plumbers and gas board officials who were called in found no trace of a leak, and inspections by the fire brigade and environmental health officers also proved inconclusive.
An autopsy on two casualties revealed they died from congestion and haemorrhaging of the lungs.
The organisers believe a boiler flue may have become temporarily blocked by leaves, causing it to emit noxious fumes.Just a question, could the area have been sprayed? Are any of those people who were there, now sick?