The story unlocks once you make your call.
True. True! Two for the gills, one for the body.
Where it came from
It sounds like a made-up fact for a quiz night, which is exactly why people doubt it.
Why it’s true
Two branchial hearts each push blood through one of the gills, where it picks up oxygen. The third, systemic heart then pumps it around the body.
The systemic heart pauses while an octopus swims, which may be one reason octopuses prefer crawling: swimming tires them out quickly. Their blood is blue, too, carrying oxygen with copper-based haemocyanin instead of iron.
Further reading
- Wikipedia: Octopus (Circulatory system)