I wasn't even sure if I really wanted to upload this, as it is without a doubt, crazy and weird.
But I did go through the effort of making it, so might as well show it.

Function Animation (Mild Graphic warning = Biologyclass level graphic as it's a diagram)

Here I came up with the Idea of a Gas-Cartridge powered inflation dart, and wanted to further work on that Concept, so I made this.

It's a dart, that upon impact compresses a shaft to pierce into a Gas Cartridge releasing the gas into the system. The gas mixes with a Glucose based Foaming agent, which is then expelled into the Target. Filling them up locally around the penetration spot which can migrate to other bodyparts if enough of it is applied.
Short after impact, the foam mixture fills 2 inflable sections up, creating a Seal that also prevents the Dart from being pulled out.

My thought behind this Dart is that it is designed to hit spots of thick skin, such as upper thighs, ass, belly and chest, maybe also upper arms.
There may be different Needle/plunger attachments for use on different areas or for Manual application.

Feel free to let me know what you think