Singapore English exhibits consonant cluster processes that fall into three types: vowel epenthesis, consonant reordering (metathesis, copy), and consonant lenition (fricativization, place assimilation, deletion). These processes are remarkable in two ways: they occur in systematic free variation within and across individuals, and they result in systematic opacity: epenthesis is opacified by reordering, which is opacified by lenition. We present two main findings. First, we provide evidence that segment reordering arises through the interaction of perceptual constraints and Output-Output Faithfulness. Second, we examine several optimality-theoretic approaches to opacity (Output-Output Faithfulness, Comparative Markedness, Stratal Optimality Theory) and conclude that none of them covers all aspects of the problem.