#needs native check

"爪楊枝" and "噛む" are written more often with kanji.
Unless you want to emphasize that he was biting it, "爪楊枝をくわえていた" sounds much more natural.

Thanks. I guess 'chewing on' and 'had in his mouth' are the same sort of thing in Japanese?

I'm not sure---I never have that habit. What about in English?
The verb that hit upon me when I saw these pictures was "くわえる" anyway.
http://images.google.com/search...n+a+toothpick"

Yep, definitely pictures of "chewing on a toothpick". くわえる it is, then. :)
Sometimes I forget about くわえる when I'm speaking Japanese, because we just don't have any regular English verbs with that same meaning to translate from. I should try to use it more, I think.

Maybe I've misinterpreted the English. Isn't Tom constantly moving his mouth as when you're chewing a chewing gum?

tommy_san,
No, not as much as with gum. He's pretty much just squeezing it with his teeth, and maybe rotating it and squeezing it some more. (At least, that's how I do it.)

CK,
Thanks for all those awesome pictures! I think くわえる is my new favorite Japanese word.

@MethodGT
I see. Then it's definitely not "噛む", it must be "くわえる".

Maybe you could try translating these sentences:
http://tatoeba.org/eng/sentences/show/2249879
http://tatoeba.org/eng/sentences/show/2249880
http://tatoeba.org/eng/sentences/show/2249881