Mongooses or Mongeese?

My Jamaican friend says,
     "It's GEESE, mahn!"

But I can't tell whether that's
     a Mon-guess [or a guess, mahn!]

I'd prefer a non-guess
     on the mongoose's gees-i-ness,
     lest I develop lexical queasiness.

It seems like it should be mongeese, 
      because "mongoose" is very
      much like "goose."
 [As my Jamaican friend would say,
      "It's jus wit the 'Mon,' mahn!"]

On the other hand, a mongoose 
      don't look like no goose I've
      ever seen.