As a child's language and vocabulary grows, they may struggle to locate a particular word or sound. Normal dysfluency occurs in developing children as a repetition of whole words or phrases while the child searches for a particular thought or word. Around age three-and-a-half, children may compulsively repeat words or phrases. This tends to fade by the time the child is five. Stuttering, in contrast, results in repeated or prolonged speech sounds or syllables. Often, involuntary blocks in fluency will be accompanied by muscle tension due to frustration. The mouth may tighten up or the eyes may blink rapidly. A child may become so embarrassed by stuttering that they talk as little as possible to avoid the struggle. This may have serious academic and social implications. The cause of stuttering is unknown, yet widely debated. Most theories suggest emotional, psychological, or neurological origins. Psychological treatment aims at improving the self-image of the child and the child's attitude toward the problem, while other therapies attempt to increase fluency by modifying the rhythm and rate of speech (Boone 316-29, 335–38).