Long time ago at Desaru, one of my friend stepped on a black urchin, there were at least 10 broken spines on his soles. The locals told us to use slipper to hit the sole until the blood flow out. For 10 mins we did nothing but whacked his sole until the blood came out. After that he just felt alright, no more pain at all- quite a miracle. If not, I was told that the pain will came up till your hair level.