Many novice programmers fail to comprehend source code and its related concepts in the same way that their instructors do. As emphasised in the Decoding the Disciplines (DtDs) framework, each discipline (including Computer Science) has its own unique set of mental operations. However, instructors often take certain important mental operations for granted and do not explain these 'hidden' steps explicitly when modelling problem solutions. A clear understanding of the underlying cognitive processes and related support strategies employed by experts during source code comprehension (SCC) could ultimately be utilised to help novice programmers to better execute the cognitive processes necessary to efficiently comprehend source code. Positioned within Step 2 of the DtDs framework, this study employed decoding interviews and observations, followed by narrative data analysis, to identify the underlying cognitive processes and related support (though often 'hidden') strategies utilised by a select group of experienced programming instructors during an SCC task. The insights gained were then used to formulate a set of important cognitive-related support strategies for efficient SCC. Programming instructors are encouraged to continuously emphasise strategies like these when modelling their expert ways of thinking regarding efficient SCC more explicitly to their novice students.