Narrative Connection
How these two moments in the story relate
Why These Connect
The narrative assertion
"The retreat of the Tesh on Level 37 due to the fail-safe's emergency lighting sets up the immediate hostility Leela faces, which directly leads to her urgency in rescuing the Doctor and the subsequent realization of Xoanon's telepathic assault. The Tesh's retreat also indirectly forces Leela and the Doctor into closer confrontation with Xoanon's forces."
About Causal Connections
A directly causes B. The first event sets forces in motion that produce the second. These are the load-bearing connections of plot--remove one and the story structure collapses.