And don't tell anybody about it, either.
2 seconds sound clip from the Back to the Future Part II movie soundboard.
You can hear this line at 01:10:14.910 in the Blu-ray version of the movie.
Quote context
[...]
- All right, pops. What's the gag? How did you know what the score was gonna be?
- I told you. It's in this book.
- All you gotta do is bet on the winner, and you'll never lose.
- All right. I'll take a look at it.
- And don't tell anybody about it, either.
- Oh, and there's one more thing.
[...]