I cut out generous size circles of batting. I used bamboo batting, but Warm & Natural or felt or any other batting that does not shred easily when pulled should work. I wanted the circle to be large enough that I could hold my fingers on it as I moved the eye about under the pressure foot. Afterward I trimmed it really close to the embroidered area.
A face needs a smile to go with those eyes. Purple rickrack was suggested but I chose a blue instead, the better to match the eyes. I rejected red because it looked very garish and almost blood-like - not really the friendly vibe I was going for. I wanted a consistent placement and curvature for the smile so I pressed into service part of a set of longarm quilting rulers I got as a Christmas present this year from my son and daughter-in-law. This was not their original intended use but, hey, I try to take advantage of versatility wherever I can. I set the height at either end by the intersection of the block piecing and choose a radius that gave me a smile that I liked. I drew a light line with a mechanical pencil at the bottom edge of the arced ruler. I counted eight peaks for each length of rickrack smile. I lined the peaks along the drawn line and turned under the raw edges at the corners of the mouth when I sewed it on.