Activate Trigger once

Hey guys so I am working on a Horror game and i have a section where when the player is walking through i have a trigger set up so when they walk through it a dead body appears out of nowhere and falls infront of them for a scare. My only problem is everytime you walk out of the trigger and go back in it makes another body fall ontop of the first one. I only want the tirgger to activate one body and after even when you walk through the area again the trigger doesnt activate anymore, but to where you can go back and forth if you need to without anymore bodies appearing.

Attach a script to your trigger object that contains a boolean such as hasBeenTriggered. Set that value to false by default. Inside of the OnTriggerEnter() function, when the trigger happens, send a message to the script controlling your dead bodies to fall in front of them. Then inside the same OnTriggerEnter() function, before it finishes, set your hasBeenTriggered to true.

Sample code:

//this is a script attached to your trigger in the level that drops the bodies
bool hasBeenTriggered = false;

void OnTriggerEnter(Collider other){
    if(hasBeenTriggered)
      return;

    hasBeenTriggered = true;
    deadBodyGameObject.SendMessage("DropBodies");
}