Galaxy-galaxy mergers are responsible for some of the most spectacular events in the cosmos. In this talk, I will discuss the impact that interaction-induced gas flows have on a galaxy before the final merger. With one of the largest samples of close galaxy pairs in the nearby universe, I will show how these gas flows affect star formation, metallicity and nuclear activity. I will compare the magnitude of these effects to the less ostentatious, but more common gas inflows due to galactic bars, in order to weigh-up the relative importance of hierarchical and secular processes.