To ancient man, a swirl was the depiction of a snake. The snake was revered as a wise creature with mystical powers. As long as man was kind to the snake, the snake would protect him from harm, keeping small rodents away from his food source.
The snake was viewed as a high ranking god, below the sun god, but the highest of all animals. Therefore, the snake, or swirl, is seen on the majority of Trypillian eggs, and has carried ove its symbolic "protection from evil" meaning to modern Pysanka desings.