Pop tarts in the UK are rather repulsive biscuit/cake things filled with jam and junk is either rubbish or drugs ( nuch the same thing IMO).
It seems to me this scene is not about sex at all - it's about gradually coming to know and trust another hiuman being, which neither has much reason to do given the backgrounds they come from. It's that magical time when you're sicovering someone to whom you can talk completely openly, without being ridiculed, someone who will listen and understand, someone to whom you are important, someone you can trust.
And I don;t know about animal sex either - FNIT may be animalistic, but SNIT isn't nor the wrestling scene, the motel, the later shots of them asleep together in tent. In all those they're doing the very things that differentiate us from animals - caring, showing tenderness and gentleness, enjoying closeness, being sensual as well as sexual.