A chemical reaction is when two chemicals (reactants) form to make a new chemical substance. During the chemical reaction, the atoms are rearranged to form the aforementioned new chemical substance (products).
There are different types of chemical reactions, however, in this definition, I will not be explaining them.
Guy 3: Woah, did you see that chemical reaction?
Guy 1: Hell yeah I did!
Guy 2: I wonder if we could do it again?
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"