Both musicians and programmers have expectations when they read music scores or source code. The goal of these studies is to get an insight into what will happen when these expectations are violated in familiar tasks. In music reading study, we explored eye movements of musically experienced participants singing and playing on a piano familiar melodies either containing or not containing a bar shifted down a tone in two different keys. First-pass fixation durations, the mean pupil size during first-pass fixations and eye-time span parameters were analysed using linear mixed models. All three parameters can provide useful information on the processing of incongruence in music. Furthermore, the pupil size parameter might be sensitive to the modality of performance. In the code reading study, we plan to explore incongruence in familiar code tasks and its reflection in eye movements of programmers.