The count of mutations Mutant generates per subject is, in Schirp's opinion, a better complexity measure than cyclomatic complexity — which is hard to compute faithfully in Ruby because the control flow is not aesthetically assessable. Separately, when taking over an unfamiliar class, running Mutant with no killed tests can be used purely as a refactoring aid: the reduction-operator output shows valid transformations; the first refactor commit can simply apply the ones with no proof of value, then public-interface tests can pin behaviour before a deeper refactor.