Originated from the 70's superhero cartoon Spaceghost where a space monkey character named Gleek from the planet Exxor would often spit from under his tongue. The word 'gleeking' was derived from this action.
"Nice going, Gleek. I didn't think anything could stop Super-mouth! Your gleeking has once again saved the universe!"
When an extremelyanimated person speaks and emphasizes their words by moving their head rapidly from side to side. This movement is similar to the neck movements of geese when they walk.