I only learned this past summer that one cannot assume that something called vegetarian Pad Thai is actually vegetarian. Restaurants that earnestly tell you that it has egg, in case you are vegan, won't think to tell you that there is fish sauce, made from dead fish. I was about to buy street food Pad Thai at the Lowell Folk Festival last summer, and when I automatically asked whether it was vegetarian, the young woman at the booth mentioned the fish sauce. After that I started asking, and thus far only the vegan restaurant we frequent leaves it out - I've asked at several mainstream Thai restaurants, which seem to include it without thinking.