- You'll instantly be transported to 1885, and those Indians won't even be there.
- Right.

7 seconds sound clip from the Back to the Future Part III movie soundboard.

You can hear this line at 00:17:48.368 in the DVD version of the movie.

Quote context

[...]

- I get shot on Monday the 7th, so you have five days to locate me.

- According to my letter, I'm a blacksmith, so I probably have a shop somewhere.

- All you have to do is drive the time vehicle directly toward that screen, accelerating to 88 miles an hour.

- Wait a minute. Doc, if I drive straight towards the screen, I'm gonna crash into those Indians.

- Marty, you're not thinking fourth-dimensionally.

- You'll instantly be transported to 1885, and those Indians won't even be there.

- Right.

- Well. Good luck for both of our sakes.

- See you in the future.

- You mean the past.

- Exactly.

- Happy trails, Marty!

- Ready, Marty?

- Ready!

- Set!

[...]