When building the sauce make sure that the pan is off the heat to avoid scrambling the eggs, the hot spaghetti and pasta water will cook the eggs enough to make the sauce safe to eat. If you forget to save the pasta water or run out of pasta water, no worries, you can use lukewarm water in its place and you will still have a similar result. Pasta water is full of starch that helps thicken the sauce without adding flour.