growth question from this tutorial

[Alida]

hi guys

here in this tutorial, i dont understand why or what the test by neighbour is doing with a particle group. can somebody explain this to me?
what is the thinking behind it?

https://youtu.be/_20NVuuZlAQ arround 9 min

thank you

[dr_ron69]

seems to me that the other video is "a version" of following tut:

https://www.youtube.com/watch?v=anQEXPlC31c