An expression similar "oh my God" or "Jesus Christ." It is used to convey shock or just inserted into a sentence and hope that people catch your drift or as I like to say get your squanch.
When an extremely animated 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.
The way that woman was yelling and geesing at her man, it looked like an episode of Jerry Springer.