You can stop, clear, and restart using the menu items. Almost immediately, the grain begins to rotate clockwise in response to imposed dextral simple shear, as indicate by the offset of the central line. The rate of rotation is half the shear strain rate of the background away from the grain. The grain also shrinks in diameter as a result of dynamic recrystallization around its periphery. When Sigma is selected, recrystallization is fast compared with rotation rate.
Recrystallized tails shown in blue begin to grow from the top right and bottom left sides.
They are swept away into the matrix at a rate that depends on their distance from the flow plane. If only one tail is considered its shape resembles a Greek letter sigma and so it is called a sigma-shaped tail. Now select Delta under the System menu and restart. This time, the mantle begins to grow as before but the rate of recrystallization, represented by the difference between the red circle and its grayed initial size, is much slower. After a while, note the difference in tail geometry.