Animating the Hearts
The hearts beat in sequence to circulate the blood. Begin by unhiding the heart and circle groups and hiding everything else. Rotate the circle group so it is lined up next to the hearts for convenience. Then open both groups and select the second smallest heart.
Animate the radius of the second circle so that it enlarges at frame 7 and returns to the original radius at frame 15. In the track bar, shift clone the key at frame 15 and drag it to frame 75.
In the track view, select the Radius parameter of Circle 2 and then click Function Curves. (Note: the 4th key should be at frame 75.)
Straighten the function curve by selecting the 3rd and 4th keys by right-clicking on them and changing their controllers to linear.
Open the Param Curve Out-of-Range Types dialog box. Then click Cycle.
When you click OK, the function curve turns into the repeating pattern of a heart beat.
In Edit Keys mode, stagger the heart beat keys so that each one begins and ends in sequence.
Play the animation in the viewport to see the result.
Animating the Skin
Worms move by stretching out and then pulling their tail end toward their head. You animate this movement using a combination of free form deformation and morphing.
In the Front view, shift-clone the skin in the -X direction so that the clone is one length behind the original. Remove the Normal modifier (so that the normals of the copied skin face outward again) and then collapse its modifier stack.
Apply and FFD Box modifier and set the number of control points as follows:
Animate the control points in five stages, 50 frames apart, starting at 0. Make a copy of the object each time:
Continue animating and cloning the worm skin until you reach the original. Make sure the last copy aligns perfectly.
Select the first copy that you made of the worm skin and create a Morph object. Assign each of the copies in sequence as morph targets.
Select the morph object in the track view and assign it a Visibility track.
Add 3 visibility keys: at frame 0, the frame where the worm skin aligns with the original, and a 3rd about 100 frames later.
Assign keys 1 and 2 to a visiblity of 1 (100%) and key 3 to 0. View their function curves:
Assign linear controllers to key 1 - Out and key 2 - In and Out.
The final curve should look like this:
Group the original skin with the veins, hearts and digestive system. Assign the group a visibility track.
Make the group invisible until the morph skin aligns with the original. Then gradually make it visible.
Animating the Digestion Process
The worm moves forward and ingests the dirt. Then bulge moves down the digestive tract with the food.
Create a Displacement space warp and align it with the food.
Link the Displacement space warp to the food.
Give the space warp some strength.
Bind the Earthworm group to the space warp.
Animate the worm so that it moves through the food and consumes it.
When the food capsule emerges from the tail, animate the base parameters and Noise parameters so that it comes out long and smooth.