I never really understood this in the movie. No blood on the ground...
Guess you never read the book, then. Coppola had to leave a lot out from the book, including how this scene got set up. Coppola had to leave so much out, he left enough material for the sequel.
Want to know why Woltz was so pissed at Hayden at the dinner?
Want to know happened to Sonny's goomah after his death?
More about Johnny Fontane's career (and why Sinatra tried to stop the movie's production)?
About the doctor who played a very significant part in the book, left completely out in the movie?
How Michael found out about Vitelli (who bombed the car)?
Why Michael fell for Apollonia so hard? And then why he rekindled a relationship with Kay?
Where Neri came from, why he was tied to Michael?
Why Don Tommasino was so big a part of the Godfather's life, and why the Godfather was so bothered by Luca Brasi?
All that and more...
It's all in the book.