This afternoon crowds of mermaids and sea creatures descended on the British Museum to fight off evil pirates and a wicked kraken.
Don't worry if you're a bit confused: this is so much more than a flashmob just getting their jollies.
Instead, they are environmental activists protesting against BP - who support the British Museum's "Sunken cities: Egypt's lost worlds" exhibition. The under the sea message makes a bit more sense now, right?
The flashmob, or "splashmob" as they call themselves, are demanding an end to oil sponsorship in art and culture.
For the flashmob's climax, the kraken (a thinly-veiled symbol for BP) was unleashed, and the merpeople united to fight it.
In case you weren't already convinced that this was an extraordinarily well prepared flashmob, they even came prepared with songs. Yep, they wrote lyrics targeting BP to popular songs like Disney's "Under the Sea" and "It's Raining Men".
This isn't the first time there have been protests against BP's sponsorship. When the "Sunken Cities" exhibition opened in May, Greenpeace activists scaled the museum and hung protest banners off its columns.
In August, hundreds of famous faces in art and science - led by actor Mark Rylance - signed an open letter demanding that BP's new five-year arts sponsorship deal be cancelled.
We very much doubt this will be the last we hear on the matter.