I have heard Japanese speakers say “Ah…soo” meaning “Ah…yes” or “Oh…really” or “Ah ha!” “Soo” in Japanese roughly translates into “yes.”
A sample conversation:
Me: “The sushi bar that we went to last night was in Soho.”
Japanese Brother-in-law: “I thought it was in Covent Garden.”
Me: “No, it was in Soho.”
Japanese Brother-in-law: “Ah…soo.”