Yeah, the bacteria generation is random so sometimes you do get parts where it's all the black bacteria. One of the "phases" was designed to have mostly black bacteria so you would have to carefully poke in between them to get to the other ones. Maybe the numbers could have used some tweaking.
Also yeah it does end after the toothbrush appears at the wall. I guess it makes it seem like there's going to be more stuff at the wall. Really the wall is quite useless and more of a distraction to be honest.
Thanks for playing and for the feedback!