Toss the tomatillos in the blender jar, then add the cilantro, half the chiles, the onion, garlic, and salt. Blend until the salsa is very smooth, at least 1 minute. (It takes a minute or so for the blades of the blender jar to catch chopped raw tomatillos. Once they do, all the ingredients will be pulled toward them. Be patient, and do not add any water. If the tomatillos don’t liquefy after a minute or so, stop the blender, prod them with a wooden spoon, and try to blend again. The tomatillo seeds will still be visible when the salsa is properly smooth.)