In article
s.com, MIG writes

[about Daleks]
I dunno. They are supposedly cold and logical, but if they spent less
time hysterically screaming "exterminate" and actually fired their
weapons, I'm sure they wouldn't get thwarted so often.

ISTR that when they first appeared they frequently fired them,
indicated by the (black-and-white) picture going briefly negative.
Perhaps that stopped when colour TV became common.

--
Bill Borland