Whilst playing in a river in Western Australia recently, two children found something almost as good as a Kinder egg. But instead of chocolate it was an old tennis ball. And instead of a surprise toy, there was a deadly animal inside. Still fun, right?

Octopus Stack 2016 04 08

Perth local Kristy Edgelow and her sons were out enjoying the weather in the suburb of North Fremantle when they found an old, split tennis ball floating in the Swan River, which flows through the city. All seemed fine and well, but after a bit of playing, one of her sons noticed something wasn’t quite right.

"My older son noticed something moving inside. We got the fright of our lives when this little fellow popped his leg out and we realised it was a blue-ringed octopus," she told PerthNow. That's a pretty appropriate response considering the blue ringed octopus is one of the deadliest marine animals in the world!

One of four species in the genus Hapalochlaena, the octopus produces a toxic venom that can kill a person in a matter of minutes if untreated. That said, the creatures are considered relatively docile, and are not known to attack unless provoked. More often than not, fatal bites occur when the tiny octopuses are accidentally stepped on.

As for what the creature was doing in the Swan River, local organisation River Guardians says the sighting is not unusual. "The river there is very [salty], so we can expect that these may be as common as they might be in the ocean," the team writes on Facebook. "These are cryptic animals that like to hide in crevices. Old tennis balls, shells and discarded containers provide perfect habitat for them."

Living throughout the Pacific and Indian Oceans, blue-ringed octopuses can be found from Australia to Japan. When they're not playing hide-and-seek in old tennis balls, they like to hang out in tide pools and around coral reefs. 

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Top header image: saspotato, Flickr