I understand the confusion. I am saying that in the imaginary Thrive world where there are other microbes swimming around arbitrarily far away from the player, every so often, a microbe will swim across the boundary of the area of interest even if the player is stationary. To simulate that, every so often, an entity will spawn just inside the area of interest while already moving, even when the player is not moving. Without this feature, if the player was stationary, and there were no spawned microbes, the player would never encounter another microbe.