This is the 4219th most frequent French word.
déclenchant
Triggering.
In this context, 'déclenchant' conveys the idea of instigating a natural or emotional response as a result of the situation (the intensity of the movie).
Le film a été intense, déclenchant toutes sortes d'émotions chez les spectateurs.
The movie was intense, triggering all sorts of emotions in the viewers.
In this sentence, 'déclenchant' is used to describe the act of causing something (the alarm) to start or be activated.
Il a appuyé sur le bouton, déclenchant l'alarme.
He pushed the button, triggering the alarm.
Here, 'déclenchant' illustrates the initiation of an event or series of events caused by the action described (the smile).