Creator David Milch was notorious for working on scripts until the last minute, which meant "it was a foregone conclusion we wouldn't be able to learn our lines," the character actor Stephen Tobolowsky wrote in an essay for Backstage magazine earlier this year. "Ian McShane told me to keep looking at him, stay in character and just call out 'Line.'" The scene became a "standoff of two actors saying, 'Line'" — with the prompts edited out of the final product.
Hilarious. I'd love to see some of these outtakes. From an article documenting all the various ways actors memorize their lines.