Reese Witherspoon has played so many 'love interest' roles that it's hard to believe she'd ever refuse to kiss a co-star, but there were exceptional circumstances on the set of 'Water for Elephants.' Her co-star was Robert Pattinson - which for the majority of women would be considered to be a bonus - but unfortunately for Pattinson, Witherspoon, and the whole production, Pattinson was trying to deal with a heavy cold at the time the scene was due to be filmed. Witherspoon wasn't keen on catching it!
A sympathetic Witherspoon later commended Pattinson for continuing to film while so ill, but also said that he had the most 'disgusting, green, infectious' cold she'd ever seen in her life. Pattinson felt wretched about the whole thing, and apologized to Witherspoon between bouts of sneezing and snotting. Nevertheless, they eventually decided the movie had to have the kiss, and so they went ahead with the scene. We'll go ahead and assume there were no tongues involved.