By the way, ignore my rediculous sewing and try to do it better than me. I really, really suck at it!
Step 1: What you need.
1. An old t-shirt, sweatshirt, sheet or other scrap of material you have lying around (I used a t-shirt).
4. (optional) needle and thread.
Step 2: Shaping the Material
If using a T-shirt, cut off the sleeves, then cut up both sides of the shirt. Then, open out the flap and you should have a rectangle with the neck hole in the middle.
If using just a sheet or peice of material just cut it into a rectangle, proportions depending on the animal(twice as long and thrice as wide as the animal).
Step 3: Filling the hole (t-shirt only)
look at where the nec hole is. fold a flap of which was the back of the T-shirt over the hole and sew along the fold, closing the hole.