Mutation analysts has emerged as a standard approach for empirical assessment of testing techniques. The test practitioners decide about cost-effectiveness of testing strategies based on the number of mutants the testing techniques detect. Though fundamental rigor to empirical software testing, the use of mutants in the absence of real-world faults has raised the concern of whether mutants and real faults exhibit similar properties. This paper revisits this important concern and disseminates interesting findings regarding mutants and whether these synthetic faults can predict fault detection ability of test suites. The results of controlled experiments conducted in this paper show that mutation when used in testing experiments is highly sensitive to external threats caused by some influential factors including mutation operators, test suite size, and programming languages. This paper raises the awareness message of the use of mutation in testing experiment and suggests that any interpretation or generalization of experimental findings based on mutation should be justified according to the influential factors involved.