you can see this for yourself by commenting out line and running the program for in range( tilesizeanimationspeed)animate the tile sliding over checkforquit(displaysurf blit(basesurf( )if direction =updrawtile(movexmoveyboard[movex][movey] -iif direction =downdrawtile(movexmoveyboard[movex][movey] iif direction =leftdrawtile(movexmoveyboard[movex][movey]- if direction =rightdrawtile(movexmoveyboard[movex][movey] pygame display update(fpsclock tick(fpsin order to draw the frames of the sliding animationwe must draw the basesurf surface on the display surfacethen on each frame of the animation draw the sliding tile closer and closer to its final position where the original blank space was the space between two adjacent tiles is the same size as single tilewhich we have stored in tilesize the code uses for loop to go from to tilesize normally this would mean that we would draw the tile pixels overthen on the next frame draw the tile pixel overthen pixelsthen and so on each of these frames would take / th of second if you have tilesize set to (as the program in this book does on line then sliding tile would take over two and half secondswhich is actually kind of slow email questions to the authoral@inventwithpython com