The sound made mentally when one reads an unpronounceable name in any type of text. The voice reading aloud goes into a spasm when coming across the word, and instead pronounces it 'rtbuigha', no matter what letters are contained in the aforementioned name.
Clouds of smoke and ash have appeared above the volcano Eyjafjallajökull recently.
*voice reading in head*
Clouds of smoke and ash have appeared above the volcano rtbuigha recently.