This example shows how the control of geometry attributes in houdini allows to tweak every aspect of a simulation in sops, before the actual sim. In this case to grow a trigger attribute across the geometry.
The bricks turning red are actually getting a true value on a trigger attribute, and therefore being activated in the rigid body simulation.
This is probably the most common use of sop solvers in houdini, feeding the previous frame geometry values to the next one. The grow effect can be based in height, distance, connectivity, transferred from an object,…
You can find the example scene here.