you say "ouch", i say...

I've always been amused by how people in different countries express pain differently. It's not a sadistic trace of mine, just curious observation.
I was used to scream "ai!" back in Sao Paulo. Now that I live in Singapore, I alternate between "ouch" and "ai". I haven't noticed exactly when I use one or the other, I guess it depends on the occasion or type of pain (still have to do more "research" on this, but am kind of reluctant to do so).
I find it fascinating that even this apparently instinctive reaction is actually culturally molded.
I found this great story on NPR, "Ouch! The language of pain", where they set out to hear people from different cultures and how they express pain. You can listen to it here.