[orangecat]

Feeling pain can't be explained as an interaction of physical particles.

Because no such explanation can exist, or because we don't have a sufficient understanding yet? See "God of the gaps".

[RivieraKid]

Because physics doesn't even have the language to describe the feeling of pain. Similarly, physics doesn't have a language to describe how "green" looks, it can only describe the frequency of green etc.

Also have a look at http://en.wikipedia.org/wiki/Qualia, it's basically what I'm talking about.