Episode 19 of The Witness opens in a room behind teal glass, in front of a panel with a blue two-by-two outline on it. Almost the whole video goes into that one panel. Once it falls, a second one follows, and a blue line leads out through the marsh to a red room full of new panels.
The two-by-two
Two panels sit side by side. The left one already has a blue line through it. The right one has yellow block shapes in three corners and the blue two-by-two outline near the top. "Okay, so now we actually have a 2x2 indication. This is the kind of stuff I like because at least I can figure out what the rules are."
The commentary calls the blue shapes negations. "When it's a one-by-one negation, it's a lot easier," but "this one actually has to be a two-by-two." Shape after shape goes into the grid, and the yellow shapes "aren't ones that we can rotate." After a few minutes: "It sure got complicated." The commentary asks for no hints, "unless I'm like, 'Please give me a hint.'"
Some wrong lines make the shapes flash an error and some don't, and the commentary can't yet say why.
The solve
Close to fifteen minutes in, a line from the bottom left over to the top right corner lights the panel white.
The commentary explains it: the shapes overlap in one spot, "and so my negation shape was put here," taking out the overlap. "Wow. Okay, next."
The checkerboard
A third panel switches on beside it, with a yellow checkered shape in the corner. "This is the last one of this particular little section." There is no two-by-two negation this time, "but this checkerboard is also really complicated." A few tries end with "Back to the drawing board," until a line zigzags around the whole grid and lights it: "Yes!"
Out to the red room
A blue line runs out of the panel and along the wall. Basket climbs stairs out into the marsh, where the line runs along a channel past a box on a track. The commentary notices a path was pushed one way earlier, "so now I can't get over there."
The line leads down into a dark red room with a row of new panels. "Okay, great, another room for us to work on." This one "doesn't seem too bad," but there are "no indicators of success or failure on this thing." Then a try flashes red marks on the narrow panel: "Okay, there we go, failure."
Where it ends
The narrow panel and the one beside it both end up with blue lines, and the view settles on the larger third panel, still undrawn. The video cuts to the end card there.