How to consistently take a picture using a voice command Using a samsung galaxy s8, android version 8.0

I'm able to occasionally take pictures with "take picture" but it works about 25% of the time. If in selfie mode with the front camera and the camera app has identified a face with a yellow circle, "say cheese" seems to work about 33% of the time.
ok it turns out the actual commands are "smile", "cheese", "capture" or "shoot" to shoot a video.