It’s a mystery as hard to grab hold of as the slippery serpents supposedly at its centre: were the 43 unidentified eggs found in a sandpit at a school on the New South Wales mid-north coast snakes, or something less sinister?

Snake social media went into meltdown on Tuesday when reports emerged that wildlife rescuers had been called in to remove a dozen mystery eggs from a sandpit at a school near the coastal town of Laurieton, 350km north of Sydney.

The eggs caused a stir when they were widely reported as belonging to one of Australia’s deadliest reptiles, the eastern brown snake.

But now doubt has been cast over whether they were snake eggs at all, with experts questioning whether a snake could bury its eggs in the sand.

Volunteer wildlife rescuers Yvette Attleir and Rod Miller from the group Fawna were called to inspect the sandpit after students found about 12 eggs in the sandpit at St Joseph’s Catholic primary school.

But the rescuers discovered no fewer than seven nests hosting a total of 43 eggs, a new addition to the list of unsavoury things found in a children’s sandpit.

The rescuers initially thought the eggs could belong to water dragons, but determined they were brown snake eggs.

“I believed they were brown snake eggs due to the fact that they were seen in the area and that when I shone a light through the egg I saw a small striped baby snake,” Miller told the Guardian Australia.

But sceptics on social media questioning the shape and location of the eggs soon forced a clarification from the volunteer wildlife rescue group.

On Tuesday Fawna wrote on Facebook: “Some experts far more experienced than our local handler have pointed out that the eggs can’t be brown snake eggs.

“When we found the eggs we carefully checked the eggs over and found that they contained what appeared to be snake hatchlings.

“We were told was there were a couple of sightings of large brown snakes behind the area and all we could surmise is that they were brown snake eggs.”

So what were they? Eastern brown snake? Water dragon? Bolivian tree lizard?

It’s become a vexing question.

Bryan Fry, who specialises in venomous animals and is an associate professor at the University of Queensland’s school of biological sciences, initially told the Guardian he believed they were “definitely” snake eggs.

But after further consideration of the fact the eggs were buried in the sand, he decided it was more likely that the eggs belonged to water dragons.

“I reckon they are indeed water dragon eggs,” he said.

He said the fact the eggs were buried in the sand was “inconsistent with snakes but entirely consistent with water dragons”.

“The large number of eggs also points towards water dragons,” he said.

Stephen Mahony, a herpetologist at the Australian Museum, said it was impossible to accurately identify the eggs from photos, but said burying eggs in sand “is inconsistent with the egg deposition behaviour of most Australian snakes”, particularly larger snakes such as the eastern brown.

He said burying eggs was “more consistent with reptiles such as dragons or turtles”.

Miller later told the Guardian that after the negative pushback on social media, he had inspected the eggs and found an “undeveloped foetus” in an unhatched egg which “looked like a small pink worm with a couple of eyes which I can only think was a snake as it had no limbs”.

He said he was unable to take a photo of the foetus because he became caught in a large hailstorm.

But the wildlife rescuers would not say what happened to the rest of the hatchlings, other than a cryptic “we’re pro-life for animals”.

“We’ve been abused after rescuing snakes in the past,” Attleir said.

One of the most venomous snakes in the world, brown snakes are highly adaptable and often find themselves in populated areas.

Increased sightings were reported across western Sydney in 2017, probably as a result of increased urban development.

Female eastern brown snakes do not guard their nest after eggs are laid and juvenile snakes are totally independent.

Brown snake hatchlings can vary widely in size, but begin to show characteristic signs of aggression soon after hatching. The eggs were due to hatch within weeks.

Catholic schools in New South Wales reopen after the summer holidays on 30 January.