We study the simultaneous test effectiveness and efficiency improvement achievable by Strongly Subsuming Higher Order Mutants (SSHOMs), constructed from 15,792 first order mutants in four Java programs. Using SSHOMs in place of the first order mutants they subsume yielded a 35%-45% reduction in the number of mutants required, while simultaneously improving test efficiency by 15% and effectiveness by between 5.6% and 12%. Trivial first order faults often combine to form exceptionally non-trivial

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... higher order faults; apparently innocuous angels can combine to breed monsters. Nevertheless, these same monsters can be recruited to improve automated test effectiveness and efficiency.