Deliberate mistake: When Susan falls through the floorboards of Mike's house she uses the nearby towel to try and get the dog Bongo to help her. If you watch at the different angles the position of the dog keeps changing. When it shows Susan from behind the dog is almost right next to her face and stepping on the towel. In the shots from in front of Susan the dog is nowhere near the towel or even in the shot. This mistake looks more deliberate as the front on shots of Susan, the dog would likely have blocked her face from the camera.
Continuity mistake: When Bree, Susan and Lynette are scrubbing the road, a red sports car zooms past them. Lynette stands, hurls abuse and throws her scrubbing brush at the car which can be seen bouncing off the car and down the road. She then kneels down and continues to scrub with the brush.
Continuity mistake: As Susan tries to get the dog to help the second time you can see the towel Susan tried to use to get the dog to help her. The shot then shows Susan and the towel has disappeared. After a quick shot of the dog it cuts back to Susan and the towel has reappeared.
Answer: He was investigating the lead not the case.