These cues can be events or people that resemble or symbolize a part of the trauma. For example, seeing a person who looks like the perpetrator or a windy day after a hurricane, or an authority figure.
Smells can be a strong trigger as well, for example smelling gasoline for someone in a car accident. Triggers can be physical sensations, for example, feeling dizziness in survivors of head trauma.
When a person is triggered, they go on high alert, the fight/flight/freeze system is activated and they can feel panicky or on edge. In those moments it is important to practice grounding skills to bring themselves back into the here and now, as well as self-soothing skills such as encouraging self-talk, listening to calming music, etc. Sometimes it is necessary to simply get away somewhere they feel safe and then engage in their coping skills.
It is also helpful to realize that the brain is operating as though the person is in a life or death situation, and so they may not seem to be acting rationally. Be supportive of people in these situation and patient, the rational brain may take some time to come back on-line and for them to tell you what is going on.
One of the most important things for survivors to do is to have a plan for what they can do to ground and sooth themselves when these things occur. Be prepared, have reminders, carry with you your soothing and grounding resources.