Bonini (2009) has recently written an interesting paper dealing with the structural setting and relationships to seismicity of a CO2(carbon dioxide)-driven mud volcano, called Pieve S. Stefano (PSS), located in the Northern Apennines of Italy.We outline here that PSS is not a mud volcano at all. The author erroneously attributes the term ‘‘mud volcano’’ (also featured in the title of the article) to a CO2-dominant gas manifestation, which should be considered as a ‘‘mofette’’ or more generally a dry CO2-vent (or ‘‘gas pool’’; Minissale et al., 2000; Heinicke et al., 2006). Our comment does not dispute Bonini’s data interpretations and conclusions (for which a first comment has already been made by Collettini, in press), but discusses why misuse of the term ‘‘mud volcano’’ may lead to misquotations in future mud volcano literature.