Stammering sounds are a type of speech disorder characterized by involuntary repetition of syllables, words, or phrases. The two most common stammering sounds are 'ERS' and 'UMS'. 'ERS' is an abbreviation for the sound 'er-er-er', which is a repeated sound made when a person is struggling to find the right word. 'UMS' is an abbreviation for the sound 'um-um-um', which is a repeated sound made when a person is hesitating or pausing in their speech. Both of these sounds are indicative of a person who is stammering.