"L’écologie? Il est tombé dedans quand il était petit!" (Ecology? He fell in it when he was small!)
Those of you who are familiar with Astérix and Obélix will know that this is a reference to Obélix the Gaul. Obélix has superhuman strength and never needs to drink the magic potion before a fight with the Romans because he fell in the magic potion cauldron when he was a little boy. The expression was part of a conversation that I was interpreting two days ago and is now very common in French. It is used when one wants to say that someone has a such a real passion for something that it has been a major part of their life, often from a very young age.
I had to think fast, and I think I came up with something like "He’s absolutely passionate about ecology". Having had time to reflect on it, I think I have a slightly better translation : "It’s in his blood". It’s a physical image that refers to the body, just like the magic potion is meant to be physically part of Obélix.
It’s a shame I can’t go back, but I think that’s the main difference between interpreting and translating: there is so little time to think when you’re interpreting that it’s acceptable to concentrate on conveying the meaning and not worry too much about the form.