Sewing together?

How-to Questions
1

I’m making Grass from Mochimochi Land: http://mochimochiland.com/weblog/?p=58

I’ve knit my pieces and felted them but I’m not really sure how to sew them together.
The directions sound like the seam will be on the outside.
The pieces shrunk significantly so I’m afraid using the actual yarn to knit them together as the seam would be too obvious.
I’m thinking embroidery floss could work, but I’d have to find colors that match…
Or should I use the clear thread?
Or am I reading the directions wrong and the seam is actually on the inside?

2

With wrong sides facing each other, sew the two halves of body together with mattress stitch, stuffing with polyfil as you go.

The Mattress stitch seam is worked from the outside and leaves the seam inside as you go, and should not be obvious at all once finished. You will use the same yarn to do the seam.
See video here on mattress stitch, Under finishing.
http://www.knittinghelp.com/knitting/basic_techniques/misc.php