I have 3, all 'assegai wood' with the distinctive pale sap wood and dark heartwood, it's Curtisia dentata. A hard very strong dense south african wood. one is like your snake one, but spiral fluted not snakes. They are, as you note, heavier than water. One has a slender shaft and a spherical head, the other has a smooth almost teardrop transition to the head like your other one. The head of a Zulu Impi would carry an iwisa (english: Knobkerrie) with a small head as his badge of office, he didn't need a larger combat head on his. I also have a few of the larger headed weapon ones.