What is the first instance of evidence tampering (inadvertent), and who does it?

As they are examining an unfinished quilt, the men return and tease them for their foolishness, asking them if the blanket was quilted or knotted. After they leave to inspect the barn, Mrs. Hale again resents the men's patronizing manner, but Mrs. Peters apologetically defends them. They find one block of the quilt that is much less tidily made than the others, and Mrs. Hale decides to fix the sewing, although Mrs. Peters does not want to touch the evidence.