Bill waved to his neighbour, Sean, from across the street, pointing out his driveway.
"Looks like you've had a nasty oil leak there, Sean. Nasty stain on the driveway."
Sean shrugged. "I guess."
Bill strolled over. "I know a thing about fixing that, clear it right up."
"Don't bother, really." Sean said, firmly.
Bill stood over the stain and looked closely. "It's no trouble. Hey, this must have dried a while ago, doesn't even have those rainbow hues any more."
Suddenly, Bill felt a sharp blow to his head and fell.
Close up, the stain had a distinctly reddish hue.