It's what the highway boys use to cut down weeds and whatnot.
7 seconds sound clip from the Sling Blade (1996) movie soundboard.
You can hear this line at 00:13:28 in the Blu-ray version of the movie.
Quote context
[...]
- I seen Jesse Dixon a-layin' on top of her.
- He was having his way with her.
- I picked up a Kaiser blade that was sitting there by the screen door.
- It's what the highway boys use to cut down weeds and whatnot.
- I reckon that didn't quite satisfy me.
- My mother, she jumped up from there and started hollerin':
[...]