These three Legionnaires are walking through the desert under a baking sun. They're fully equipped with enough water for days and food aplenty.
On the shimmering horizon, mirages come and go and come again. They see visions of swimming pools attended by dusky maidens and stalls full of ice creams and sorbets of every conceivable flavour. But the Legionnaires do not crack. Instead they keep marching solidly on.
Suddenly one of them freezes. "Psssst," he says. His companions halt and strain their eyes to where the first Legionnaire is pointing.
"Le voila," he says, "Regardez, mes amis, isn't zat a bacon tree on ze 'orizon?"
And sure enough, there it is, proud and defiant in the middle of the desert, a true bacon tree. Slowly they creep forward towards the far off mystery object. Inch by inch, centimetre by centimetre, until they are within a stone's throw of the bacon tree. Ever nearer they creep, until suddenly a shot rings out, dropping one of the Legionnaires in his tracks. The other Legionnaires hit the ground as bullets thud into the sand around them.
The other two return fire and give first aid to their wounded companion. Even as they bandage him and pour water over his face they can hear his faint voice. "Zat was no bacon tree," he gasps, "Zat was an 'am bush."