What is brain freeze?

First, an analogous... analogy.  There are signs on most bridges warning of ice.  The reason for this is that, while regular roadways are protected from fast changes of temperature because these quick changes don't penetrate the ground very quickly, on a bridge, both the top and the bottom are exposed to the air, so they will be colder and freeze faster than roads insulated by the ground. 

Image from zachronen.co.il

The mouth is similar with regards to "brain freeze."  Obviously, the brain doesn't freeze.  The picture above shows a lot of internal areas of the head and neck.  Between the oral and nasal cavities is the hard palate.  When you're eating cold foods or liquids, the first part of each swallow includes the tongue pushing the bolus (food or liquid that's chewed and ready to swallow) against the hard palate and back towards the back of the throat.  Since the hard palate has cold items against its bottom side, and air passing through the nose on the top, it is not well protected against temperature changes. 

So it gets cold.  And this is what a "brain freeze" really is.  I don't know of any advice to get rid of it.  I close my mouth and keep my tongue against the hard palate, which should provide some insulation and help to normalize its temperature faster. 

To prevent brain freeze I have two suggestions.  1) Don't eat or drink cold things.  and 2) If you do eat cold things, keep them moving around in your mouth until they are warm before swallowing them.

An SLP versus A SLP

It's an historic moment... well not really. For me at least. But using "a" versus "an" is a question and a bit of a pet peeve of mine. I haven't 'looked up' the correct usage, but I'm gonna say how it is on my own authority. Because you know me... the all knowing and all and such and whatnot and that. Read at your own risk...

The only reason that "an" exists is that there are words that start with a similar sound to "a." If you were to say "I want a apple" at a conversational speed, it would sound like "I want apple." It sounds like you aren't using the article "a." As far as I know, no one denies that this is the reason for the existence of "an." That extra letter N helps us understand that a speaker is using the article "a"

Picture from theblogofrecord.com

Now lets move to SLP. It starts with an S. Why does it sound better with an "an"? Well, because S doesn't start with S. S starts with "eh" Two parts: "eh" and "s". S So you could say "I'm a speech therapist," or you could say "I'm an SLP." Personally, I wouldn't say or write "I'm a SLP." Even when I do say it, I tend to put a little pause (glottal stop) between a and SLP. Another example might be university. You wouldn't say an university. It's a university. Because university starts with the y sound, which is a consonant.

Picture from askaurinal.com

Spanish has similar rules. If you use o (or in English) before a word that starts with o, you change it to u. Agua is feminine, but the water is "el agua" because if you were to say "la agua," it would sound like one word.

In the modern world, language takes oral and written forms. An SLP sounds better, while a SLP may be said to look better. The written form is a reflection of the oral form, and in my opinion, should follow changes in the oral form.

Picture from skiptucker.blogspot.com

As far as "An history", this clearly breaks the "Use 'an' only before vowels" rule. I'm not sure how it gets justified, and I don't really care. As far as I'm concerned, it's "a history," and others can do what they want. At the end of the day, the purpose of language is almost always communication, and either form communicates the information.