sewplease, yes, I use a walking foot. And the serpentine stitch allows for a bit of error - I use a 3mm width so it isn't too wide, and about the same length. And glad you liked the pattern of the mystery.
Someone asked about different sizes of blocks. Sulabug used her 4" blocks -- she cut the squares for the flying geese at 2-1/4" square and the rectangle connecting sections at 4" x 11". Those who want to use 5" blocks, the geese squares would be 2-3/4" square and the rectangles 5" x 14"