Quote Originally Posted by Artanis View Post
Even if Astartes don't get scared, I would think they would be able to tell when something is scary to normal people, even if only so that they can better anticipate how quickly nearby Guardsmen will start getting shot by their Commisar require morale boosts.
It's a fairly simple test. If a marine ever has:
i) lots of enemies to kill, or
ii) cause to think "gee, this is going to suck"

It's going to be scary for regular, non-gene boosted meatsacks.

If both i) and ii), it's going to be really scary, but probably not for very long.