in the military before we started class the instructor would often show a funny video or an unfortunate video on the topic at hand to gain students attention. By bringing out the emotions such as joy, anger, fear in the learners, they can see a new aspect of the subject at hand. for example, when we learned about improvised explosive devices, we were shown videos of people killed or wounded by these weapons or videos of blowing up washing machines for training. these gave us a better appreciation for the power of explosives far better than a simple lecture with facts and numbers. Granted these are extreme examples I have found none the less that they are effective in gaining attention in the classroom and may be used several times through out the period of instruction to help maintain attention. by switching the videos content from comedy to tragedy or reverse it keeps the students involved as long as they are appropriate for the students age maturity level and content of the course.