Since most of these children do not stutter as adults, this normal stage of speech development is usually referred to as pseudo-stuttering or as a normal disfluency. As children learn to talk, they may repeat certain sounds, stumble on or mispronounce words, hesitate between words, substitute sounds for each other, and be unable to express some sounds. Children with a normal disfluency usually have brief repetitions of certain sounds, syllables or short words, however, the stuttering usually comes and goes and is most noticeable when a child is excited, stressed or overly tired.