A short while ago, I was on vacation, and ate several times at a Vietnamese sandwich shop (in North America) that served what were presented as traditional Vietnamese style sandwiches.
While most of the ingredients were self-explanatory, one of them was something I've never tasted or seen anywhere else: it was a sandwich spread with a light(?) grey color, and a slight texture similar to a thin sort of pate. The pate was a bit sweet to taste, but otherwise didn't taste familiar (not obviously fishy/beefy/chickeny, etc.).
From what I understand, pate and similar spreads are common in Vietnamese cuisine, but I'm having a hard time narrowing the possibilities down further to ones that match the above description.