ELM time series from TCV Ohmic H-mode plasmas are analysed in order to extract information on the ELM process. Firstly, signatures of a chaotic behaviour called unstable periodic orbits become visible when particular plasma conditions are reached. Secondly, the ELMs are sometimes synchronized with the sawteeth activity. The dependence of the phase of the synchronization and the ratio of the ELM frequency to the sawteeth frequency on the plasma parameters is described.