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We present an XMM-Newton imaging spectroscopy analysis of the galaxy cluster A1644. A1644 is a complex merging system consisting of a main cluster and a subcluster. A trail of cool, metal-rich gas has been discovered close to the subcluster. The combination of results from X-ray, optical, and radio data and a comparison to a hydrodynamic simulation suggest that the subcluster has passed by the main cluster off-axis and that a fraction of its gas has been stripped off during this process. Furthermore, for this merging system simple effects are illustrated that can affect the use of clusters as cosmological probes. Specifically, double clusters may affect estimates of the cluster number density when treated as a single system. Mergers, as well as cool cores, can alter the X-ray luminosity and temperature measured for clusters, causing these values to differ from those expected in equilibrium