Sometimes when we aren't too sure what we, uh, intend to say, we, um, pepper our speech with all sorts of strange sounds. This is a universal habit: Americans say uh or um, the Spanish eh, and the Japanese eeto or anoo. A pair of psychologists now report that, far from distracting the listener, these seeming nonsense sounds improve the clarity of speech. Herbert Clark of Stanford University and Jean Fox Tree of the University of California at Santa Cruz find that conversation carries two simultaneous streams of information. The first is the actual content of the words. The secondthe uhs and umssignals the pace of the speaker's thoughts. After analyzing hours of recorded conversation, the two researchers discovered that uh tends to precede a minor pause in talk, and um a major one. More surprising, Clark finds that um-sprinkled talk is easier to comprehend, perhaps because the filler sound alerts the listener that an unusual word or idea is on the way. But woe betide the politician who allows such terms to intrude. "When I say uh and um in conversation, I'm saying 'I'm not ready to go on.' If you're a public speaker, you don't want to be telling your audience that," Clark says. A case in point: Not a single uh or um appears in the recorded inaugural speeches of American presidents between 1940 and 1996.