Careful, accurate observation is one of the most important tools for scientists. It is not always easy to do, especially if you are trying to keep your eye on several things at once. That is one of the reasons that scientists work so hard to limit the variables in any testing. If only one thing is changing, it is easier to focus on the changes.
You can test your skills of observation with the following video:
After watching the video, watch it again, this time using your skills at observation to watch for things that change. How many changes can you spot? Keep a list, and once you think you have spotted them all then go to next page.