Is it a plane? No, it's probably a defecating duck.
The Civil Aviation Authority, more used to investigating aircraft crashes, is heading into a "season" where it is asked to investigate houses, mostly in rural areas, being splattered with foul-smelling material, sometimes up under the eaves.
Some people have asked whether the offending substance could have come from aircraft toilets.
The CAA has been investigating such complaints since 2003 and it is referring people to a report published on its website.
The report rules out aircraft toilets, which can only be emptied on the ground. The deodorant chemicals would leave a tell-tale blue streak on the hull and nothing along those lines had been reported.
If an aircraft developed a hole large enough for solid waste to escape it would lead to rapid depressurisation and an emergency situation.
Tests of the substance also showed no sign of the toilet chemical, but they did indicate the strong presence of sterol, a steroid associated with human waste.
It was a "curious result" but a probable explanation could be that waterfowl are known to feed in various waterways and ponds, including wastewater ponds.
A former Department of Conservation biologist Murray Williams pointed the finger at nesting waterfowl desperate to get rid of a build-up of excrement away from the family home.
He said during the nesting season, roughly between August to October, the female will generally sit on her nest for most of the day without defecating - leading to a greater liquid content in the excrement.
The duck, swan or goose will deliberately not defecate near her own nest and will fly some distance before releasing up to a cup of waste, he said.
"When released, the excrement is therefore both voluminous and very runny, as well as having a foul, almost putrid, smell."