If you've ever wanted to add puff balls of yarn to things, here's how. Some examples of potential applications are shown in the first couple of slides. Bunnies need tails, of course, but some or your winter hats may also be happier with some puffs.
Step 1: Step 01. Materials
We only need yarn and a can (or some other kind of object to cast the yarn around). As you get more experience, you can use pretty much anything, and will get better at calibrating the radius of the object for the desired puff result.
Step 2: Step 02. Casting the yarn
Wrap the can with the yarn, holding the yarn in place for the first couple of rounds. Keep wrapping until you get to desired thickness. (Don't be stingy! The puff will be pitifully unfluffy if you don't use plenty of yarn on this step.)
Step 3: Step 03. Removing + preparing the yarn
Remove the bundle of yarn from the can, and snip the end.
Then, cut a short piece of yarn and tie around the middle of the bundle, as shown. Double knot.
Step 4: Step 04. Cutting
Start with one end of the figure eight you now have, and cut the loop in half. Flip yarn around, and cut other side in half. You should end up with a big shaggy bunch of yarn.
Step 5: Step 05. Trimming
Start at the edges, and begin trimming the shaggy puff down. You'll feel like you are just hacking away at it for awhile, but have patience, and you'll start to see it become more puff-like. (It's kind of like giving someone a haircut - cut slowly, in small increments.) Depending on how much yarn you've used, the consistency of the yarn itself, and the radius of the object you've cast around, your puff ball will already have a predetermined optimum diameter that it will look its best at. Make sure to take breaks between trimming and fluff the whole thing up so you are giving it an even trim. When you are done trimming, you should more or less have a puff as shown.
Step 6: Step 06. Attaching the puff
In this example, a puff is attached to a mitten. You can affix puffs to pretty much anything, but it's easier if the object you are attaching to is knit (it has big holes through which you can weave the yarn).
First, using a crochet needle, locate the place where you want to attach the puff. Then, poke from inside to outside, and grab one of the ends of yarn from the puff, and pull through to the inside. Poke through the mitten nearby (but not in the same place) from inside to outside, and grab the other end of the puff, and pull through to the inside. Now you should have both ends of the yarn on the inside of the mitten, but not through the same hole. Knot the yarn on the inside (double or triple), and snip the ends. If you are doing this for a hat, or for something else where you don't want the yarn ends sticking out, you can weave the ends into the knit material. Otherwise, you are done! Now you have a mitten with a puff...