Well, we don't really know.

4 seconds sound clip from the Night of the Living Dead (1968) movie soundboard.

You can hear this line at 01:20:22 in the Blu-ray version of the movie.

Quote context

[...]

- Well, there's no problem. If you had a gun, shoot 'em in the head. That's a sure way to kill 'em. If you don't, get yourself a club or a torch. Beat 'em or burn 'em. They go up pretty easy.

- Well, Chief McClelland, how long do you think it will take you until you get the situation under control?

- Well, that's pretty hard to say. We don't know how many of 'em there are. We know when we find 'em, we can kill 'em.

- Are they slow-moving, Chief?

- Yeah, they're dead. They're all messed up.

- Well, in time, would you say you oughta be able to wrap this up in 24 hours?

- Well, we don't really know.

- We know we'll be into it most of the night, probably into the early morning.

- We're working our way toward Willard, and we'll team up with the National Guard over there, and then we'll be able to give a more definite view.

- Thank you very much, Chief McClelland.

- This is Bill Cardille, WIC TV 11 news.

[...]