This post is part of a series, so if you haven't read the first six posts, here are the links!

Part 1: General factsPart 2: Types of tramaPart 3: Aspects of trauma that make it more or less likely to have lingering psychological effectsPart 4: Individual factors that make it more or less likely a person will develop PTSD after a trauma
Part 5 A and B: Developmental trauma (some thoughts on Nobody But Us by Kristin Halbrook) and an interview with Kristin herselfPart 6: Intrusive Recollection
As we think about this, let us put on our writerpants, because portraying this well in fiction is all in the details. 
If you've read all the posts, you know I have a lot of admiration for how Kristin Halbrook showed how her characters' traumatic pasts altered the way they saw and experienced the world. Here's yet another quote from Nobody But Us:

We got music on and sugar highs from drinking Coke when we enter Utah. The mountains are a nasty reminder of Colorado and pain that came quick and the smell of burning skin.

For so many people, the sight of the mountains inspires awe or admiration. Most of us enjoy that view. It's pleasant and peaceful. Not for Will from Nobody But Us. What I love about this very simple two sentences is how Will isn't trying to remember what happened to him. He actually doesn't ever try to think about it because ... why the hell would he want to do that?!? [see more about this in my very next post] But the sight of the mountains triggers this sensation (pain) and then a scent memory. It's not overdone--it has impact, in fact, because it's so matter of fact and therefore startling.

A trigger can be anything. ANYTHING. A sight. A sound. A physical sensation. A scent. Even another memory. You have so many choices. You can drill down as deep as you want. You can stretch into the periphery for distant associations or a string of connected cues. Your options are nearly endless, so I suggest you don't go for the obvious.

My mentor, a psychologist who's an expert in treating trauma and spent many years working at a VA hospital, once told me about one of his patients, a former soldier, who was walking through a park on a sunny day and had a full-blown panic attack. A park! A beautiful day! He didn't know why he'd had that reaction. But after some discussion, they realized what had triggered it: a drop of sweat trickling down the side of his face.

Sometimes it is that small, that simple, that devastating. When humans are in crisis mode, our focus narrows and our perceptions are altered. It's a little like walking through a field of burrs--some of them will stick, and others won't. Some will fall off, and some of those little devils will somehow get so deeply embedded that it really takes effort to pry them loose. If you took the time to consider a particular fictional trauma from my second post, review those notes now! What pieces of that experience will embed themselves in your character's memory only to ambush him/her later?

Below is one of the most effective passages I've come across in YA that shows a character being triggered. I could tell you exactly why I think it works so well, but think I'll just leave you to chew on it for a while. Feel free to comment on why it's effective (or why you disagree--it's okay if you do!):

Our frog lies on her back. Waiting for a prince to come and princessify her with a smooch? I stand over her with my knife. Ms. Keen’s voice fades to a mosquito whine. My throat closes off. It is hard to breathe. I put out my hand to steady myself against the table. David pins her froggy hands to the dissection tray. He spreads her froggy legs and pins her froggy feet. I have to slice open her belly. She doesn’t say a word. She is already dead. A scream starts in my gut—I can feel the cut, smell the dirt, leaves in my hair.~SPEAK by Laurie Halse Anderson