hypothetical desert

HOLDEN   You're in a desert, walking along in the sand
       when....
LEON     Is this the test now ?                              
HOLDEN   Yes.   You're in a desert, walking along in
       the sand when all of a sudden
       you lookdown and see a.....                               
LEON     What one ?   
       It was a timid interruption, hardly audible.
HOLDEN   What ?                               
LEON     What desert ?                               
HOLDEN   Doesn't make any difference what desert..
       it's completely hypothetical.
LEON     But how come I'd be there?                             
HOLDEN   Maybe you're fed up, maybe you want to be
       by yourself.. who knows.
       So you look down and see a tortoise.
       It's crawling toward you....