In Changi Village in the 60s and 70s when you started to bargain for some item the first thing the local trader would do was look at your knees.
If there were no hairs on them it meant that you had been recently wearing long trousers so you must be a new, and therefore, inexperienced arrival.
Hairs on your knee indicated that you had been wearing shorts for some time so was likely to know the correct price to pay.