[ Vader was watching the dancers with a naked hunger - and envy. Especially some of the more experienced ones, even following a few to better observe them. Enough ship he didn't see Obi-Wan and walked straight into him. It wasn't especially hard - he wasn't walking fast after all, but he was heavy and sold. Vader made soft sound at the impact - part annoyance and part surprise - before grabbing at Obi-Wan to right him. ]
III