Did your wall have cracks that you planned to fix, but now they're gone? You suspect an April Fools' Day trick, but it's probably not one. Here's why: During winter, heating dries the air which causes dry, itchy skin. Reduced humidity dries your home, too, causing some parts to shrink. And during winter, cracks in walls and separations in trim and woodwork begin to show up and, as things get drier and drier, hairline cracks grow and become more noticeable. Thus, winter and early spring are the best times to find and patch such cracks. When warmer weather arrives, homes are opened up, humidity levels rise and they start reabsorbing moisture, causing your house to expand again, too. And cracks that were visible start closing up again, disappearing as if by magic. For more tips, visit our Web site at onthehouse.com. And that's the On The House tip for today.