Why was 6 afraid of 7?

He looked up from the floorboards, and found himself under 7.

An admittedly improper position for him, but 6 saw the proof he wanted: 9’s body, half devoured.
7 was a cannibal…
7 8 9.
6 has spent the remainder of his days terrified of 7, worried that someday 7 will learn what 6 knows…
And promptly solve his problem.