 The scene in which Will Smith (I) (qv) drags the unconscious alien  across the desert was filmed on the salt flats near Great Salt Lake  in Utah. Smiths line, "And what the hell is that *smell*?" was  unscripted. Great Salt Lake is home to tiny crustaceans called brine  shrimp. When they die, the bodies sink to the bottom of the lake  (which isnt very deep) and decompose. When the wind kicks up just  right, the bottom mud is disturbed and the smell of millions of  decaying brine shrimp can be very very bad. Apparently, nobody  warned Will.