It seems like the average senna lifespan is longer than that of the universes it inhabits. This large, snake-like creature has somehow evolved a form of inter-dimensional travel to escape the inevitable heat death of most universes. Sennae are unfathomably large, sometimes stretched across three or four universal dimensions when fully extended. These mysterious creatures have no known predators nor prey. Eons ago, people used to believe they could see sennae traveling through distant universes in the night sky, but science has long since "proved" that such a sight would be physically impossible given their size. History debates the authenticity of several allegedly-verified sightings.