Well, I have a few inventions that I plan on making sometime soon.
1. A watergun that instead of pumping water into the pressurized canister by hand, you wear special shoes with pumps attached to them, so every time you step you pump more water into the chamber. You could build up really powerful water blasts that way without much effort.
2. I was looking online about hormones and came across some very interesting ideas. Someone could in theory, make a pill that would make someone want to be friends with someone else. Basically if someone is being mean to you, give them a pill and they would be nicer. I wont state the hormone used, as it might be held against me. Also another invention in hormone pills would be the hormone MSH, which if I could figure out a way to get the thalamus, (or hypothalamus, not sure which one produces it yet) to produce MSH I could make a pill that gave people tans. No more Tanning salon.
3. I had this other idea about a new type of fishing trap, but it's kinda hard to describe, (not to mention fishing is over productive as is) so I'll leave it at that.
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I tried to build a new variation of a flamethrower once
Heehee, i've actually made a grenade launcher, and accidentally blew up part of our shed fastening a homemade grenade. (Using a gerber baby food jar, gasoline, and some special stuff that youll have to read the anarchists cookbook for

) Bottom line, I suggest that you don't make weapons at home.