Noses. It's why linguistics refers to "m", "n" and "ng" as "nasals" - labial, dental, and guttural, respectively (depending on the position of the tongue and whether the mouth is open or closed). All sounds that can be produced by human speech can be classified by how the mouth produces it. Ignoring glottals, stops and tonings (important in some African and Asian languages but not found in Indo-European languages which includes English), consonants are plosives, hisses, aspirates, laterals and nasals, further classified as labial, dental, guttural or palatized, voiced or unvoiced. Greek and English have a further peculiarity, the "theta" with is technically a hiss but with the tongue between the teeth. Either unvoiced as in "thin cloth", or voiced as in "these clothes" (JRR Tolkien, Professor of Linguistics at Cambridge University as well as the daddy of all fantasy writers). Vowels fall into a completely different category, but its TL;DR - if you're interested, read Wittgenstein like I had to.
