Dvojice vrubounů, jak valí kuličku z trusu (foto Hectonichus (Own work), CC BY-SA 3.0, https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons).

Dvojice vrubounů, jak valí kuličku z trusu (foto Hectonichus (Own work), CC BY-SA 3.0, https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons).