Yes right! There is a audio lesson of this 3 bears song like George mentioned.
Tim used 히쭉히쭉, though.
Sometimes, We sing this song with 으쓱으쓱.
I think you heard "으쓱으쓱" which is a mimetic word.
The meaning is "motion of lifting the shoulder up and down".
Imagine when a baby is acting cute like a dance they learn from school.