Originally Posted by
Lament
Maybe because foreigners don't want to have the runs on a daily basis ...
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You can surely get the runs from pad thai: dried shrimp, the sauce, chives, bean sprouts etc all have potential to do that. And obviously the hygiene of the cart/establishment plays a role.
I've found that as familiarity with Thai foods as a whole, and the ability to know dishes and order them, increases people generally move away from the dish.