Pourquoi tu parles en anglais maintenant?

Today I started tutoring one of my French students (let's call him Pierre) after a looooong summer break. My French is out of practice and his English is out of practice -- it made for an interesting lesson.

Me: Okay, Pierre, what is on this card?
Pierre: La glace!
Me: Yes, but in English. Do you remember?
Pierre: Urrhhhm, la glace!
Me: Remember, it's ice cream.
Pierre: Ice creeeeeam.
Me: Do you like ice cream?
Pierre: Yes.
Me: What's your favorite kind? Which ice cream do you like?
Pierre: Chocolat! Vanille!
Me: Chocolate and vanilla?
Pierre: Yes.

"Pierre" spent most of the lesson repeating single words after me and saying yes/no, but it is incredible how much he actually understands -- he simply chooses to respond in French, partially because he knows I understand him anyway. What I found most amusing was what he asked me about a half hour into our lesson while we put together a pirate jigsaw puzzle:

Pierre: Pourquoi tu parles en anglais maintenant? (Why are you speaking in English now?)

As if he'd only just noticed that I'd stopped using French.

Words I learned from Pierre today:

Pirate crochet - Captain Hook
le gribouillage - scribble drawings
les serpentes au beurre - snakes in butter

I don't know about the last one, but he insisted that he had "serpentes au beurre" for snack at school today. On second thought, maybe it's legit, because this is what I found upon typing it into google.fr.