The assassination scene itself is a piece of sweet freakness. It creeped me out the way Bully does when Brad Renfro runs up and clumsily jabs a knife into the back of Nick Stahl.
This is after the first - and only - blow onto Trotsky's (Burton's) head with a pickax.... his eyes beginning to bug out, giving Alain Delon (the assassin) an Et Tu Brute? icy glare.
Ew... but it's the scream that sells it. It's a yelp right there in between anger and anguish, and I had to rewind it because it didn't sound human.
I realized that the scream is actually a combination of both Burton and Delon's yelling. Delon, as studly as the guy is, possesses a pretty feminine scream.
I think what extended the creep factor for me is that Burton keeps walking around even though he has a huge puncture wound in his head. And again... that look! If you could videotape someone's life flashing before their eyes, then that is what their expression would look like.
This final shot is reminiscent of the massacre scene in The Battleship Potemkin. I'm betting this was on purpose since Losey was a student of Eisenstein. Maybe it was an homage, or maybe it's just influence seeping through.