A random, and possibly dense, SPN trivia question

I've seen in several places recently a reference of Dean's fear of rats. And for the life of me, I can't figure out where this notion comes from. I assume I'm missing some canon point of trivia, so if anyone can point me to the appropriate episode and scene to answer the question, I'd appreciate it.

Still Life - "Not Fade Away" - Acts I, II, & III

We're in the home stretch, folks. Here be the next-to-the-last ep (number 6 of 7). Enjoy.

( Not Fade Away, Acts I, II, & III )