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The reptilian brain is the oldest part of the brain that concerns itself with food, sex, clobbering feral cats, speaking in a caveman voice, foaming at the mouth, biting off noses, and violently ripping out the eyes of the guy next to you because he looked at your woman funny. As such, it is a very busy brain and cannot be bothered with such pointless things as emotions , philosophy,
sports origami, cuddling, or even lobsters. 
A unique feature of the reptilian brain is that as the above mentioned items (those items namely being food, sex, and danger) are mentioned repeatedly, (that is again for the hard of seeing food, sex, and
water danger) the reptilian brain begins to light up like a pinball machine, or perhaps like the laser lights at a fancy exotic dance studio...
In either case, the reptilian brain is unable to distinguish between the three kinds of stimulation, those being food sex and danger, so hypothetically, if you wanted to really, really stimulate your reptilian brain, you would eat a sandwich while screwing someone in a thunderstorm.
edit Reptilian brain and conspiracy theorists
There are those who claim that the reptilian brain is a primary tool used by the Illuminati to control the masses. Basically, the theory goes that they use the basic needs and cravings of the general public to pacify them and manipulate them into buying stuff they really don't want or need and that really isn't good for them. Such crackpot theories, however, are just ridiculous. Not only is the Illuminati non-existent, but if even if they did exist,
which they do which they don't, they would be using methods far more subtle than innuendo and visual sexuality to stimulate people into action. 
Even with an organization as supposedly secret as the Illuminati, there has to be a power struggle between members of the same secret society, complete with assassinations, manipulations, and string pulling. Sooner or later, in an environment like that, somebody would probably threaten to spill the beans. In either case, the topic of discussion is neither beans nor the Illuminati, so how about you just forget about the whole darn thing.
edit Practical uses for the reptilian brain
The reptilian brain has a variety of uses. Let's assume for example, that the rest of your brain doesn't work. The reptilian brain will help keep you alive. Most people believe this would be a good thing. Such a being, however, would be a thoughtless, eating, fucking, and killing machine, but that is the trade-off for lacking a prefrontal cortexy thingy.
Sex sells. Nuff said.
- ↑ The weepy female kind
- ↑ Mmmmm. Lobster. My mouth is watering right now. Just a little butter...and ooh a dildo with that would be wonder-wait what did I just say?
- ↑ You know, all of a sudden, I could go for some nachos...Damn what is that smell? Whatever it is...it smells good.
- ↑ They totally do. Click to go to their website.
- ↑ Okay, seriously Jesus Christ, what is that smell? It smells fucking good. It smells like steak with caramelized onions getting attacked by Indians during a high speed car chase mixed with female pussy. It seriously smells that good. Where is it coming from?
- ↑ You know NOTHING, got it?