A long time ago, in a galaxy not so far away (time and distance amount to nothing in a mythological story), the Devas and Asuras were at war. Neither were immortals and there were heavy casualities. So, the Devas decide to churn the Milk sea(Vishnu's private Jacuzzi)to get the Divine Nectar called Amrit.
So, they approach Vishnu, use Vasuki as rope, Mt. Mandara as churning rod, yada yada yada.. find it here..
http://www.balagokulam.org/kids/stories/dashavatara.php#kurma
Now, most retellings of this story leave out a very important part. As Lord Vishnu took on the form of Mohini(a very beautiful Apsara) and tried to seduce the Asuras while slyly distributing all the nectar to the Devas, two guys from the Dark side saw through his/her bluff. They were the two strapping young Asuras named Rahu and Ketu (They had their fair share of celestial nymphs and could easily spot the wolf among the sheep).
So these two Demons jump line and join into the Deva queue and Mohini busy with the clever show she was putting on, feeds the Amrit to the two. On Surya's prodding and realising her folly, she releases the Vishnu chakra(a very deadly discus) on the two and cuts their heads off.
Now, here's the interesting part. Since the Amrit had already passed by their heads and throats by then, their heads were immortal which became the stars Rahu and Ketu. These are termed in Hindu Mythology as Demon stars (Rahu.. Ketu.. Demons.. stars.. get it?). They are mighty pissed off at Surya till this day and occasionally gobble him up to create eclipses.
The Amrit, which went through their throats spilled on the earthly ground and gave seed to the Ginger and Garlic plants. Since they are born from Amrit, these two plants have medicinal properties. While the Asura qualities make them harmful at times.
TRUE STORY!!
(This story was told to me by a teacher of mine back in 3rd or 4th standard in an SUPW class. SUPW stands for socially useful productive work. We were taught to stuff like Knitting so one day we guys took a stand and refused to do any knitting in that class. The teacher decided to tell us this story to pass the time. I couldn't find this story anywhere else on the Internet and so decided to reproduce it here.
On a sidenote, I have always wondered why Mohini isn't counted among Vishnu's Dashavatar. Anybody have any idea?
ps1:
Devas->the good guys(Jedi),
Asuras->the bad guys(Sith),
Vishnu->Yoda,
Apsara->celestial nymph,
Surya->sun god
ps2: for those whom it is not obvious enough.. True Story is Barney stinson's catchphrase for all the totally far fetched stories he tells