why is there always a short pause in all dvd movies sometime during the movie?

Answer 1

The "pause" is caused by what is called dual layering. Essentially, dual layering means a disc has two layers on it instead of one. The first layer is semi-transparent so the laser reader on your DVD player can shine through it and read information off the second layer.
Why dual layering? It lets companies pack more information on single discs. A single-layer DVD has up to 4.7 gigabytes of storage space; a dual-layer disc has up to 8.5 gigabytes of storage space.
More storage space=more DVD extras and special features.
I'm sure you've noticed how many more extras and special features are put on DVDs these days? Dual layering, with its extra storage space on the second layer, allows for this.
Unfortunately, as the laser accesses the second layer to read parts of the movies we watch, this also creates the "pregnant pause" that can be so darned annoying!
Hope this helps answer your question.