Forbidden Popsicle

The Forbidden Popsicle is a suppressor that has heated up and is red hot (and therefore glowing) and due to its shape which is similar to a push-pop ice cream, it gives the appearance of a red/orange/yellow Popsicle, hence the nickname.

A suppressor, more commonly known as a silencer (which is a marketing term coined very effectively by a company), is a device that attaches to the end of the barrel of a firearm and reduces - not eliminates - the sound after being fired. It does this by trapping the gas inside little chambers called baffles within the suppressor when a bullet passes through after being fired. The expanding gases from the burnt gunpowder that have pushed the bullet forward, or are coming out of the barrel, the gun, and some of its fills into the suppressor.

If you’re using a suppressor on your firearm and you are shooting a lot of rounds through it in a short amount of time or in succession, the heat from the gas begins to heat up the metal. Eventually, it gets so hot that is causes the metal to start glowing red. This would happen to any metal when heated up; Take a paper clip and hold it under a BIC lighter, same result but from different heat sources.

And this is where the term forbidden popsicle comes from since it looks like a popsicle when it is glowing red hot.

Further reading:
Suppressors go by several names:
Silencer, Cans, Freedom Cans, awesome, & expensive lol.

Moral of the story: get a Popsicle

When firing a belt fed machine gun equipped with a suppressor, holding down the trigger and firing the machine gun long enough to make the suppressor glow orange or red hot. (Looks like an orange or red popsicle) Can result in catastrophic failure of the suppressor and should only be done in controlled environments or extreme situations. It's otherwise forbidden to do in most military applications.