The clapperboard snaps at the start of a take, so it is read as a signal that something is beginning. Dream books link it to readiness, performance and a scene about to be played.
Where in your waking life have you met something like this lately?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.