A picture and a question

First, a not very well-taken picture of my first Clessidra sock in progress. I have a friend who's going to Siberia in about a month and I wanted to make her socks that went high to her knees to keep her legs warm, as she'll be staying there for about a year and a half.


As you all can see, I'm working on the heel now. I have a question though, before I continue.
I had 36 stitches on needle 2 before I started the slip, seed stitch each row pattern. Once I've finished that, the pattern claims that I have 19 stitches on each needle, but I have 18 on each (18 +18 = 36). Did I slip incorrectly? Where do those 2 extra stitches come from?