In chapter 5 of the core rules of KULT: Divinity Lost we learn about the Horror Contract. And in this excellent (and quite unique) guide in how to portray Horror we get the following advice: Dare to be Unpleasant. Take things in different directions and further than the RPG norm when it comes to horror.
So how do you do that?
How are you Unpleasant in an interesting way?
I find that the loss of control is a very efficient way of creating tense and memorable situations. There is an example in the core rules when a Lictor uses its commanding voice on a Player Character and makes him/her lift up an infant child. And the description of how warm and soft the skin is, how it chuckles and laugh is in stark contrast to the fact that it is carried towards the oven.
Just reading that gave me chills. The good kind. What would you not promise, what would you not swear to do to let the Lictor let go of its mental grasp.
But I think there is a key learning in this. Making the players observe disturbing things is one thing. Making their characters partake in it. That takes it to a whole new level.
Why let a player watch a cannibal act if you can force the player to eat the raw, steaming meat!
So dare to involve the players. And make them partake in the gritty scenes!