In a better case, there would be additional causal edges going into the sink ... but each causal edge, as it falls in, can generate a branch pair.
Need to mark branchlike and spacelike edges
[ to do: annotated multiway causal graph ]
Everything that goes into the BH region ends up with the other member of its branch pair not going in Why can’t both members of a branch pair go into the event horizon? [ Either both members are inside the BH; both are outside; or it straddles the event horizon ]