Steph returns her attention to the road, since Marie's apparently quite comfortable and now would be a bad time to hit a pothole.

Or a body. Like the one sprawled across the road in front of them. (She can tell it's a body and not a person who's napping in the road, because of how people's legs usually both join on to their bodies.)

"Hang on!" she yelps, doing her best to swerve gently and trusting to Mel's reflexes to grab the girls.