A scenario describes how one or more system components interact to provide a certain set of functionalities. Because each scenario only represents a partial view of the overall system behavior, scenario- based specifications may hide unexpected interactions (called implied scenarios) which are not part of any scenario individually. Implied scenarios may either indicate gaps in the original scenario specification, or undesired behavior that should be avoided during scenario implementation. This paper presents a reverse engineering environment to support extraction and detection of implied scenarios from execution traces. The main contribution of the paper is to demonstrate how the concept of implied scenarios, thus far restricted to early phases of the software life- cycle, such as requirements elaboration and reliability prediction, can also be applied to support comprehension and testing of existing systems.