  We study the SZ-effect-induced non-Gaussianity in the cosmic microwave
background (CMB) fluctuation maps. If a CMB map is contaminated by the SZ
effect of galaxies or galaxy clusters, the CMB maps should have similar
non-Gaussian features as the galaxy and cluster fields. Using the WMAP data and
2MASS galaxy catalog we show that the non-Gaussianity of the 2MASS galaxies is
imprinted on WMAP maps. The signature of non-Gaussianity can be seen with the
4^{th} order cross correlation between the wavelet variables of the WMAP maps
and 2MASS clusters. The intensity of the 4^{th} order non-Gaussian features is
found to be consistent with the contamination of the SZ effect of 2MASS
galaxies. We also show that this non-Gaussianity can not be seen by the high
order auto-correlation of the WMAP. This is because the SZ signals in the
auto-correlations of the WMAP data generally is weaker than the WMAP-2MASS
cross correlations by a factor f^2, which is the ratio between the powers of SZ
effect map and the CMB fluctuations on the scale considered. Therefore, the
ratio of high order auto-correlations of CMB maps to cross-correlations of the
CMB maps and galaxy field would be effective to constrain the powers of SZ
effect on various scales.
