Blocking, which is probably what you referred to is one of the manifestations of stuttering. Symptoms: Stuttering symptoms may include: Having a hard time starting a word, phrase or sentence. Stretching out a word or sounds within a word. Repeating a sound, syllable or word. Brief silence for certain syllables or words, or pausing before or within a word. Adding extra words such as "um" if expecting to have problems moving to the next word. A lot of tension, tightness or movement of the face or upper body when saying a word. Anxiety about talking. Not being able to communicate well with others. - mayoclinic.org