Many of these ways are not found in other major Indian classical dance traditions. Kathakalī employs several methods: 1) direct without special effects or curtain; 2) through the audience, a method that engages the audience, led by torchbearers since Kathakalī is typically a night performance; 3) tease and suspense called "nokku" or "tirassila" or "tiranokku", where the character is slowly revealed by the use of a curtain. The "tease" method is typically used for characters with hidden, dangerous intentions. The play is in the form of verses that are metered and lyrical, sung by vocalists whose voice has been trained to various melodies ("raga"), music and synchronized with the dance-acting on the stage. The vocalists not only deliver the lines, but help set the context and express the inner state of the character by modulating their voice. For example, anger is expressed by the use of sharp high voice and pleading is expressed by the use of a tired tone. Music is central to a Kathakali performance. It sets the mood and triggers emotions resonant with the nature of the scene. It also sets the rhythm to which the actor-dancers perform the choreography and scenes. Some major musical patterns, according to Clifford and Betty, that go with the moods and content of the scene are: "Cempata" (most common and default that applies to a range of moods, in battles and fights between good and evil, also to conclude a scene); "Campa" music (depict tension, dispute, disagreement between lovers or competing ideas); "Pancari" (for odious, preparatory such as sharpening a sword); "Triputa" (thought-provoking, scenes involving sages and teachers); "Atlanta" (scenes involving kings or divine beings); "Muri Atlanta" musical style (for comic, light-hearted, or fast-moving scenes involving heroic or anger-driven activity). Many musical instruments are used in Kathakali. Three major drums found are "Maddalam"(barrel-shaped),"Centa"(cylindrical drum played with curved sticks) and "Itaykka" ( Idakka , hourglass-shaped drum with muted and melodious notes played when female characters perform). Over five hundred Kathakalī plays ("Aattakatha") exist, most of which were written before the 20th century. Of these, about four dozen are most actively performed.