One main hypothesis in our ongoing musical gestures research is that we often have mental images of sound-producing actions included in our perception and cognition of musical sound, e.g. listening to (or merely imagining) a passage of drumming may very well also evoke mental images of drumming gestures. Furthermore, our gesture observation studies seem to suggest that listeners tend to parse streams of musical sound into a series of goal-directed gesture-units. These gesture-units are often quite short, with durations typically less than 3 seconds in many different kinds of music. We believe these short gesture-units correspond to the smallest ‘meaningful’ rhythmical chunks in the sense that they cannot be broken down into smaller units without loosing their musical significance. The study of small rhythmical chunks is interesting, both because they are important in many kinds of music as ornaments and as texture and groove patterns, but also because they may reflect biomechanical and neurocognitive elements at work in rhythm cognition. We suspect that there are a number of biomechanical and neurocognitive constraints as well as principles for optimalization which will result in the emergence of rhythmical chunks. Biomechanical constraints concerning speed, force, fatigue, need for rests, energy economy, mass-spring movement, sustained vs. ballistic movement, etc., may contribute to the formation of such rhythmical chunks. Biomechanical constraints may also lead to coarticulation, i.e. to the subsumption of several onsets into rhythmical chunks, effectively fusing several onset actions into one gesture-unit. As is apparent from research on coarticulation in linguistics, coarticulation also has neurocognitive aspects such as anticipatory cognition and the formation of motor programs, elements which support the idea of mental processing of chunks as wholes, i.e. as integrated units present ‘all at once’ in our minds, both in perception and action. In musical contexts, gesture-unit coarticulated rhythmical chunking seem to fit well with ideas of rhythmic fluency and various elements of musical expressivity such as ‘swing’ or ‘feel’.