We need to understand the impact of side effects whenever changing complex object-oriented software systems. This can be difficult as side effects are at best implicit in static views of the software, and typically execution traces do not capture data flow between parts of the system. To solve this problem, we complement execution traces with dynamic object flow information. In our previous work we analyzed object flows between features and classes. In this paper, we use object flow information to analyze side effects in execution traces and to detect how future behavior in the trace is affected by it. Using a visualization, the developer can study how a selected part of the program accessed program state and what side effect its execution produced. Like this, the developer can investigate how a particular part of the program works without needing to understand the source code in detail. To illustrate our approach, we use a running example of writing unit tests for a legacy system.