I was using Duolingo on my netbook (no extra-fancy devices for me!). At some point during a lesson, I lost my internet connection without being notified. Rather than booting me when I tried to hit "check", the lesson continued on to completion (a good 5 or 6 questions!), although audio did not play. It told me all my answers were correct, and when I "completed" the final question, Duolingo finally gave me a loading failure page and that's when I found out I had no net. I should note that I use No-Script for Firefox, and I noticed there are more scripts on Duolingo than before. While I've white-listed Duolingo itself, I don't know which others I should enable (are you guys using mixpanel for something, for example?).