   float end3 = 70.;
 
   // Uncomment when debugging single scene
-  //return scene16(pos);
+  return scene13(pos);
 
   /* ---------- SCENES --------- */
 

vec2 scene0(vec3 pos) {
  return opU(
    heart(pos),
    bloodCellField(pos)
  );
}

/*

    // ta = camera direction (where the camera is looking)
    // cr = camera rotation
    //vec3 ro = vec3( -.5+3.5*cos(.1*a), 1.0, .5 + 4.0*sin(.1*a) );
    vec3 ro = vec3( -.5+2.*sin(1.*a), 1.+.5*cos(a), 2. );
    vec3 ta = vec3( .0 );
    // camera-to-world transformation
    mat3 ca = setCamera( ro, ta, .0 );
