Alien pod? Floating game of bubble soccer? Nope, just a bloated, dead whale.

When fisherman Mark Watkins happened upon this large "pod" off the coast of Western Australia recently, he initially mistook it for a fallen hot air balloon. A closer look, however, revealed the structure to be the inflated carcass of a humpback whale. "Seeing it was great. The smell? Not so much," he wrote on Facebook.

The animal's strange appearance comes down to the very same processes that make whale carcasses explode sometimes: the stomachs contain a lot of gas. As the sun's heat beats down, gasses build up inside the stomach as the contents decompose. But a thick layer of blubber and skin stops it all from escaping. You're essentially left with a rubber balloon that's being filled from the inside. Tick, tock ... boom!

Dead whale disposal can be difficult (something we've experienced firsthand), but in this case, the carcass will likely sink before reaching shore, some 25 miles away. For all the dead whales that hit shore, many more find their way to a watery grave.  

It can take some 30 years for a sunken carcass to decompose, a process that plays an important ecological role for the deep-sea creatures that feast on them. These so-called "whale falls" are regularly scavenged by everything from sharks to bone-eating worms. 

"We actually did have a 3.5 to 4 metre white pointer [shark] around our boat that day," Watkins told The West Australian.

Just what happened to the floating humpback remains a mystery, and as no necropsy plans are in the works, we'll probably never know. 

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Top header image:  J Maughn, Flickr