So, I watched this movie again last night..
So, one alien stayed behind on Mars in a space ship that played sounds that equated to a human DNA sequence with the last section missing.
So the first people who found it were blasting it with radar and it was the "wrong" sound (i.e. didn't complete the sequence, so it killed them).
Eventually they figured it out and played the right sequence and were able to enter the ship and the aliens were really the same as humans cuz they populated the Earth when Mars got hit by a meteor or whatever. So they were just waiting for a human to come so they could tell them story.
My question is if aliens are so f'ing smart why didn't they realize that HUMANS were outside their ship without giving them some stupid test to complete?
anyhow, it's a decent movie.. check it out if you haven't seen it.