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In many of the examples mentioned above, optical peculiarities seem to be associated with anomalies in the HI distribution within and around galaxies that appear quite normal optically unless special image enhancement techniques are used. Some of these anomalies are clearly the result of interactions or perhaps the high velocity encounters described as `galaxy harassment' by Moore et al. (1996). However, it also seems that optical diagnosis is a more sensitive indicator of recent harassment than is HI observation, though the latter technique may reveal traces of earlier interactions that are no longer evident as optical anomalies.