Given scene/plot descriptions from movies or TV shows, and given a specific question about the scene, summarize the question into a title

Example input: At the beginning of the movie Gangs of New York, Priest Vallon tells his son not to wipe the blood of the blade after he's cut himself shaving, saying "The blood stays on the blade". I've watched the movie multiple times, but can never find what the meaning behind that phrase is. Anyone able to shed some light on this?
Example output: What's the meaning behind the phrase "The blood stays on the blade"?
Example explanation: A person gives a detailed description about a scene from the movie Gangs of New York and asks the meaning of a said phase in the scene. The question is summarized as What's the meaning behind the phrase "The blood stays on the blade"? for easy indexing the next time someone searches for a similar phrase
Q: This is something very common, that we all have been seeing since as long as we can remember. This question stemmed from my recent re-watching of Django Unchained, where Quentin Tarantino makes a cameo appearnce. I have always been intrigued by this. M Night Shyamalan, Peter Jackson, John Carpenter, Robert Rodriguez, Eli Roth, and many more, have made frequent cameo appearnces in their movies. The trend goes as back as Alferd Hitchcock's movies. I want to know more about this. What are the factros behind this gesture ?
A:
Why do directors make cameo appearances in their movies?