The Flagellum was our best Biota program ever. Here we have slimmed down Ian Osgood's javascript implementation to show this one program running.
//wiki.ralfbarkow.ch/assets/pages/biota-flagellum/flagellum.html HEIGHT 230
The pink program counter turns when blocked by a blank or failing instruction. The green data counter moves under control of program instructions, copying or deleting characters as told. wiki 
See Coding Flagellum step by step.
pages/biota-flagellum