I like the bus analogy. There is another way to describe joinstr.

- An ostrich creates a nest (pool)
- Some female ostriches lay their eggs in the nest (register inputs) 
- Incubation period lasts for a few minutes (coordination using relays)
- Hatching of eggs (new UTXOs)

Eggs were of different colors but the ostriches that come out of these eggs look the same.

https://image.nostr.build/32448fd03646b76fb385e212edd92faca6a5f84f777ceef65f17c4960b4750a2.jpg