I absolutely fucking love tremors! It hit me at just the right age and I still love to throw it on every now and then. The second and third ones are pretty decent too. There is no fourth one so Im not sure why you are saying there is??
There's actually reams of writing about the original Tremors because it's actually a really well-scripted and put together movie. There's not a lot of "nothing happening" scenes. Most of the scenes are either always moving the plot forward or quickly developing the characters while moving the plot forward. There's just enough breathing room for character development, but the film always keeps its pace. It's just so tightly scripted and executed for a silly monster movie. It honestly should be mentioned more often alongside The Thing which is similarly tightly structured.
Oh yeah. In brief; Chani, and other Fremen women, dance on the sand. The longer the time between repetition, the greater their mastery. The dance is a religious rite that changes over the thousands of years in the series.