diff --git a/src/bin/flat.rs b/src/bin/flat.rs
index 3087d0d..cf94272 100644
--- a/src/bin/flat.rs
+++ b/src/bin/flat.rs
@@ -1,3 +1,4 @@
+use std::f32::consts::PI;
 use flo_draw::*;
 use flo_canvas::*;
 use glam::*;
@@ -10,6 +11,17 @@ use approx::assert_abs_diff_eq;
 
 const DT: f32 = 0.1;
 
+fn draw_loop(gc: &mut Vec<Draw>, mut pts: impl Iterator<Item=Vec2>) {
+	gc.new_path();
+	let Some(first) = pts.next() else { return; };
+	gc.move_to(first.x, first.y);
+	for pt in pts {
+		gc.line_to(pt.x, pt.y);
+	}
+	gc.close_path();
+	gc.stroke();
+}
+
 pub fn main() {
 	with_2d_graphics(move || {
 		let canvas = create_drawing_window("Refraction");
@@ -30,13 +42,36 @@ pub fn main() {
 			draw_fan(gc, &tube, vec2(-500.0, 0.0), vec2(1.0, 0.0), 1.0);
 			gc.stroke_color(Color::Rgba(1.0, 0.5, 0.0, 1.0));
 			draw_fan_2(gc, &space, vec2(-500.0, 0.0), vec2(1.0, 0.0), 1.0);
-			gc.stroke_color(Color::Rgba(0.0, 0.5, 1.0, 0.5));
-			draw_fan(gc, &tube, vec2(0.0, -0.5 * tube.internal_halflength), vec2(1.0, 1.0), 1.0);
-			gc.stroke_color(Color::Rgba(0.0, 0.5, 1.0, 1.0));
-			draw_fan_2(gc, &space, vec2(0.0, -0.5 * tube.internal_halflength), vec2(1.0, 1.0), 1.0);
 			draw_track(gc, &space, vec2(-500.0, 0.0), vec2(1.0, 0.2));
 			draw_track(gc, &space, vec2(-500.0, 0.0), vec2(1.0, 0.5));
 			draw_track(gc, &space, vec2(-0.5 * tube.inner_radius, -1.25 * tube.external_halflength), vec2(0.1, 1.0));
+
+			for y in [-1.25, -1.00, -0.85, -0.50, 0.00, 0.40, 0.70, 0.95, 1.05] {
+				let pos = vec2(0.0, y * tube.external_halflength);
+				gc.new_path();
+				gc.circle(pos.x, pos.y, 5.0);
+				gc.fill_color(Color::Rgba(0.0, 0.5, 1.0, 1.0));
+				gc.fill();
+
+				gc.stroke_color(Color::Rgba(0.0, 0.0, 0.0, 0.5));
+				draw_loop(gc, itertools_num::linspace(0.0, 2.0 * PI, 32).skip(1).map(|φ| {
+					let dir = Vec2::from_angle(φ) * 20.0;
+					let dir = space.flat_to_global(pos, dir);
+					pos + dir
+				}));
+				gc.stroke_color(Color::Rgba(0.0, 0.5, 1.0, 0.5));
+				draw_loop(gc, itertools_num::linspace(0.0, 2.0 * PI, 32).skip(1).map(|φ| {
+					let dir = Vec2::from_angle(φ) * 20.0;
+					let dir = space.flat_to_global(pos, dir);
+					space.trace_step(Ray { pos, dir }).pos
+				}));
+				gc.stroke_color(Color::Rgba(0.5, 0.0, 1.0, 1.0));
+				draw_loop(gc, itertools_num::linspace(0.0, 2.0 * PI, 32).skip(1).map(|φ| {
+					let dir = Vec2::from_angle(φ);
+					let dir = space.flat_to_global(pos, dir);
+					space.trace_iter(Ray { pos, dir }).nth(20).unwrap().pos
+				}));
+			}
 		});
 	});
 }