"Boiling oil?" I suggested.
"Almost, but not quite... boiling date oil actually."
Dates have long been a staple of the Arabian diet and were a near-perfect food for a besieged fort as they were nutritious and stored well. When stacked sack upon sack they oozed oil, which was then collected and - when needed - heated to boiling point and poured out on hapless attackers.
Within the fort walls is a labyrinth of winding staircases, false doors and more outlets for the bubbling date oil.
"What will get you here?" asked my guide as we stood at the bottom of a curved staircase. I looked up, no place for oil, no evidence of a secret door either.
Smiling he bounded up the stairs to a narrow gap in the wall which I'd totally overlooked.
"See, it's at knee-height - you'd come running up the stairs looking up or ahead and then someone would stab you or shoot you through here - you wouldn't know what hit you."
Literally cut off at the knees.
Built in the protective shadows of the fort is the souk or market- once a warren of tiny shops so small customers had to stand in the alley outside and point to what they wanted. Although the structure itself has been modernised, many of the wares have changed little over the centuries.
Entire walls glittered with the traditional Omani silver daggers or khanjar that are still worn today, shelves were piled high with the round embroidered hats that are favoured by Omani men (along with the red and white checked headscarves).
Most intriguing of all were the piles of what looked like quartz pebbles. This was frankincense - a gum resin extracted from Boswellia species trees.
Although Yemen and Somalia also produce frankincense, the Omanis have no doubt theirs is the best. Frankincense has been used as a perfume and a medicine for more than 5000 years - it is depicted on a mural in an ancient Egyptian tomb and of course is mentioned in the Bible as one of the gifts given to Jesus by the Magi.
Frankincense has to be burned to release its heady, exotic perfume, so burners, from the simple to the ultimate in bling machines, are also sold in the souk.
As I turned around from a display of the latter I was startled to find myself face-to-face with a Bedouin women whose face was almost totally obscured by a indigo-dyed mask. This left only her eyes, heavily lined with black kohl, and her chin uncovered. A ridge of fabric rather like those on a battle helmet ran from beneath the mouth to a peak above her head.
Women trade, shop and drive in Oman's deserts. But out in the countryside you're unlikely to see Bedu women outside their homes in the evening. Which is why I was the only woman drinking tea and smoking hubble-bubble in an outdoor cafe on the edge of the Wahiba Sands, a 10,000-square-kilometre expanse of dunes that stretches to the Arabian Sea coast.
It was a warm starlit night but no one was gazing heavenwards. Instead, all customers' attention was focused on the side wall of the cafe, onto which was projected a giant screening of a football game between Qatar and a South Korean club side.
Tendrils of smoke rose lazily in the air as two Moroccan waitresses wove between plastic tables and men sprawled among piles of floor cushions covered in Bedu handwoven fabrics in stripes of red, black and silver.
Parked among the late model 4WDs nearby was a small truck with a kneeling camel gazing implacably over the tailgate.
