Illustration of spurious dipole excited from higher-order moments through mask coupling. Top panel: an ideal CMB sky with identically vanishing dipole moment. Bottom panel: same realization, but with the Galactic plane masked. By accident, one large extended hotspot happens to lie on the Western Hemisphere inside the mask. Once this is removed by the mask, the net unmasked result is a dipole pointing toward the Eastern Hemisphere with an amplitude of 7.6 μK.