Anything that stimulates a threat response, usually an echo of an earlier experience which you have not finished reacting to yet. Triggers are very personal – different things trigger different people. If you were bitten by a dog when you were younger, for example, and didn’t deal discharge your body’s response to that fully when it happened, the experience may be stored in your body. If you hear a dog barking at a later stage, this might trigger you to go back to those unfinished responses, such as fear or flight.