Summarize this article in one sentence.
In order to stimulate you guinea pig into action, be sure to choose a playful, bright color of yarn. This will look more interesting to your guinea pig and will brighten up their enclosure. You also want to make sure to choose a yarn with wool that is not too thin, since guinea pigs tend to want to chew on things and thin wool won't stand up to their teeth. To do this you are going to want to find an object to wrap the wool around that is small and fairly rigid, like a small cardboard box. Keep in mind you don't want to choose an object that is too big, since this size of the box determines the amount of yarn wrapped around it, and you don't want this part of the toy to be too big. Wrap the wool around the object once and tie tightly. Don't worry if it's not an extremely tight knot, it will still work. Continue to wrap the wool around the object, with each loop approximately on top of the last. You want the toy to be thick and plush, but if you use too much wool, the toy will be too bulky or heavy for your guinea pig to play with easily. As you determine how many loops are necessary, keep in mind that the thickness of the wool loops at this stage is about half the fatness of the finished toy. Depending on the size of your object and the thickness of your wool, this should be about 15 - 25 loops. When it is thick enough, cut the end of the wool from the ball of yarn, and don't worry about tying that end off. Use a double knot, and tie it as tightly as you can. It may loosen a bit if you are doing this unassisted, but that's okay. This is where using a box or other rigid item comes in handy, as it's easy to slide the wool under. If you wrapped the wool around a rounder object, use your fingers to push the tie under the loops. Now that the body is tied in the middle, turn over the object you wrapped the wool around and cut the loops. Try to cut exactly opposite from where your tie was in order to keep the dangling wool pieces even. If your scissors don't cut through all of the wool at once, do it in sections, making sure the cuts are as straight as possible. When you are finished cutting, remove the loops from the box. You should now have a thick chunk of straight, even wool strands that are tied in the middle. Even though it will be dangling and the wool strands are tied, it is still possible for a clever guinea pig to pull loose strands out and eat them, which could be dangerous. In order to avoid this and make the toy safe, flip the body of the toy over so the middle tie is at the top. Take another strand of wool and tie this together around the bottom of the strands. You want to make sure this second tie is close to the bottom. Measure a piece of string that is long enough for the toy to dangle where your guinea pig can reach it, without being so easy to get to that it's not exercising your pet. It is recommended that you cut a piece that is too long and trim it down later as you string it up. Take this long piece of wool and tie it through the middle of the toy body. Tie the other end to the roof of your guinea pig cage, and watch your guinea pigs enjoy their new toy!

Summary:
Purchase thick wool in a bright color. Start making the body of the toy. Stop wrapping when the body of the toy is thick enough. Tie a piece of wool around the middle of the loops. Finish the body of toy. Cinch the strands in for safety. Hang the toy up and let your guinea pig enjoy!