Carefully, twist off the top of each Oreo cookie sandwich. You want to the filling to stay on one side of the cookie sandwich.
Draw a circle with green gel frosting slightly larger than the M&M candy on half of the cookie halves that have the filling. This will be the "glue" that holds the candy in place.
Draw a circle with blue gel frosting slightly larger than the M&M candy on the remaining cookie halves that have the filling. This will be the "glue" that holds the candy in place.
Place M&M candies in the center of each gel frosting circle. Press lightly to ensure that the candy holds.
Use the red gel frosting to draw on "blood vessels".
Christina's Notes
Add Spiders: Use a dark icing to make a web and decorate with a candy spider.