Fernando

 FERNANDO  is  OSCAR  ' s pet flea , whom he audition s for the Bunkam & Ballyhoo Circus when [http://muppet.wikia.com/wiki/P._T._Bunkum P. T. Bunkum ] come s to SESAME STREET in episode 1451.

 FFERNANDO   rehearse s in  OSCAR  ' s own make shift flea circus where he run s over a jellybean, leap s through a cigar band , & run s around a bottle cap. Although he can ' t be seen, his feet can be heard tapping on the surface of an aluminum plate , & he make s faint squeak y noise s.

Just to satisfy skeptic s,  FERNANDO  can also be ordered by  OSCAR  to run about the bodies of his critic s , finally putting t o rest any question o f his existence.