Ramming his tongue into Sam's mouth? Right Dean, yeah, that was totally keeping things under control and being the responsible, logical, smart one! A gold star for you!
The cabin floor was really hard and uncomfortable. Sam's knees were beginning to ache, and he was pretty sure he had a splinter in his palm. But he was worried if he pulled away and suggested moving to one of the beds (not that they were much comfier) that Dean would bolt, drive off and leave him here forever.
And so he kissed back, tongue duelling with Dean's for control over the kiss.