That's a tough question for me, because part of the reason I love Perl is all the little things that are waiting to nibble my toes. It's a rich, delightful language, and I miss it every day when I clock in to work on some overbearing Rails project.
I think the first playful nip from Perl was when I realized that I didn't need to explicitly specify scalar to get the length of a list - I could just assign the list to a scalar variable. I had already read this in the Camel book, but I stuck with scalar because I didn't trust Perl to do what I meant. I still remember the day the scales fell from my eyes, sitting in front of my Slackware machine with coffee in hand and suddenly seeing context in my Perl app where before I had seen only code.
I continued using scalar in production code for a while, mainly because my coworkers and managers didn't really grok context.
I've had many nibbles since, but that is the one sticks out in my memory.