It also might be a self-organized system composed of multiple algos from different shops: i.e. like a "Life" game. For example: one algo put a bid of X, a nano

It also might be a self-organized system composed of multiple algos from different shops: i.e. like a "Life" game. For example: one algo put a bid of X, a nanosecond later another algo steps and put a bid X+1. The first algo cancel X and put X+2, etc. Until it reaches a threshold of X+T, then all bots cancel and start again from X. You can see this behavior with human traders in after-hours sessions or in other illiquid markets. But of course in case of humans we are not talking about nanoseconds ;)