"Indian Head-Shake"

[swanwhite]

Hi there all! I have a question from my brother today. He works at a Subway which is a frequent stop for the east indian community in the neighborhood, and during his time there has noticed what he calls "the indian headshake". It usually seen as a response to a question, and instead of a yes or no, the customer does this interesting bobbing, almost figure-eight movement with their head. He's asked his coworkers (one of whose family is from India) but no one seems to know what it means.

Anyone know the meaning of this? Everyone at his Subway is dying to know... Thanks in advance!