The three sisters, Clotho, Lachesis and Atropos, are jointly responsible for controlling the clues of life. The Greeks insisted that there were three great clues. Clotho crossed the clues of life itself, Lachesis measured the clues of length, and Atropos would cut the thread to end the life. Not the most fluid theme!
Higher pay symbols are consistent with the theme, and the three sisters themselves offer the highest rewards, and then provide icons related to their personal gifts or curses based on your point of view. For example, Atropos End of Life Scissors is a good secondary bonus. There are various animation options on the slot, and fate guides you into each temple.