The project in question is here.
In the comments chain for that Instructable I noticed that people were having problems with filling their moss bombs. One of the steps involved blowing up a balloon full of beer and shredded moss with your mouth. I tried doing the project and I found it kind of gross and messy, and it seems like other people thought the same. To solve this, I made this little filler. The nice thing about this doohickey is that it can fill balloons with any semi-liquid substance, from moss bomb mix, to paint, to water. The principle of this design makes it so the balloon is full of both water AND air, which makes it spray its contents better when it pops, and makes it more likely to pop.
Step 1: Parts and tools
-a standard 12 ounce soda bottle
-a normal cheap ballpoint pen (I used a Bic)
-a hot glue gun (Well, where there's smoke, there's fire.)
-a pointy object (I used a multi-tool set on the "knife" setting)