Like most internal borders in Australia, the border between WA and the Northern Territory serves to protect from plant and animal diseases. It is strictly forbidden to carry meat, fresh fruit and vegetables into WA. On our last few days in NT, somehow we forgot about this and bought lots of fruit and vegetables. As a result, we had a salad feast and apple overdose on our last day before crossing the border...
Anyway, the border control was very friendly and pointed out some interesting birds in the surroundings of the border station!