Sarcasm without contradiction between literal and appeared meaning

What exactly is the definition of sarcasm?

As I’ve understood it, verbal irony is when the literal meaning of a sentence differs from the appeared meaning (it is opposite/close to opposite). If the irony is directed at a person in a slightly ”mocking” way, it is called sarcasm (MasterClass).

An example of sarcasm according to Literary Devices is "Zombies only eat brains. You're safe". I do not understand how this is considered sarcasm. The obvious meaning of this example is "you have no brain/you aren't smart" but then how is it sarcastic? It is only a rephrasing of the basic meaning (you have no brain). You could have added "you are safe because you have no brain", and the meaning of the sentence would remain the same, but it is implied already. The literal meaning and the intention are the same/synonymous.

It's like writing "you're not smart" instead of writing "you are stupid". The statements basically mean the same thing, they are only formulated in different ways. I understand that "you are safe" is a more positively charged sentence than "you have no brain", but does that make it sarcasm? They are still considered synonymous, not the opposites of each other?

If sarcastic sentences should be read as the opposite of the actual phrasing, then this example should be interpreted as if the person is not safe, meaning that they have a brain (since that is the opposite of what is written, but it is obviously not what is the intention of the sentence). If it is only the rephrasing that makes it considered sarcasm, then by definition "you are not so smart" should also be considered the sarcastic version of "you are stupid". It feels very strange, because the sarcastic version would be the opposite of what you mean, so in the latter example it would be ”you are smart".

It was not only this sentence I didn’t understand the sarcasm in, all the examples were just smart reformulations of criticism. In what way is this sarcasm?

Link to MasterClass: https://www.masterclass.com/articles/learn-the-differences-between-irony-sarcasm-satire-and-paradox#what-is-sarcasm

Link to Literary Device: https://literarydevices.net/sarcasm/

Sarcasm is usually employed where the literal meaning is obviously not the case.

Your statement "If sarcastic sentences should be read as the opposite of the actual phrasing..." misunderstands sarcasm. Sarcasm is not always read as the opposite; rather it can imply the opposite.

Thus "Zombies only eat brains. You're safe" is sarcastic because the person obviously has a brain to be alive, but the statement implies that's not so.

However, if a boy playing football [soccer] says to a friend "I'm going to score a goal" and then proceeds to sky the ball way over the crossbar, then the response might be "Oh yes, that was close!" That response is actually the opposite of what is meant: the ball was nowhere near close. However, it still comes within the definition of "the literal meaning is obviously not the case".

There are broader and narrower definitions. Much of what LiteraryDevices is calling sarcasm, MasterClass would call irony. (And much of what they both call irony, some would call simply being a jerk.)

• Sarcasm, narrow definition: Saying the opposite of what you mean. "Good work, genius!" (meaning "Terrible job, idiot").
• Sarcasm, broader definition: Generally using insulting, cutting, cynical humor. The Marvel character Rocket Raccoon has a sarcastic personality.
• Irony, narrow definition: Depending on a contrast for effect. "Your tireless persistence in studying archery is matched only by your consistent ability to miss the target." (This says exactly what it means, so it fails the narrow definition of sarcasm, which would have ironically praised the person's ability to hit the target. But it is surprising or humorous because the first half of the sentence is a compliment and the structure leads us to expect another, but it ends with an insult.)
• Irony, broad definition: Pretty much the same as the broad definition of sarcasm, but wittier and perhaps less antagonistic. P.G. Wodehouse's character Bertie Wooster is often accused of being ironic.

These days, it largely seems to come down to tone. A “sarcastic” statement is delivered in a sneering tone, a “sardonic” statement in a grim or fatalistic one, and an “ironic” statement with a straight face. This is not how dictionaries define these words, and you will find people who say that is not correct usage, not how those words are most commonly used, or both.

Your second link regards it as mainly a difference of intent: “Sarcasm indicates a deliberate intention to mock, satirize, or otherwise poke fun at something. Verbal irony often generates subtle, gentle humor. The outcome of sarcasm is closer to explicit criticism, direct antagonism, and occasionally intentional verbal hurt or shame.”

The word irony is used very loosely these days, with many different meanings.

• The original meaning (to quote Merriam-Webster) was, “incongruity between a situation developed in a drama and the accompanying words or actions that is understood by the audience but not by the characters in the play.” The classic example was Oedipus cursing the murderer of the former king and swearing to catch him, when the audience knew it would turn out to be he himself. This is now often called dramatic irony.
• It often is extended to scenes whose true meaning is revealed in a twist later (such as what Charles Foster Kane in Citizen Kane was trying to recapture for his entire empty life). The characters don’t realize it at the time, but whether the audience does depends on whether this is the first time they’ve seen the story.
• From there, it was extended to events in real life that Wikipedia calls, “ironies of Fate.” That is, if you imagine history as a drama being watched by a spirit who knows exactly what will happen, any decision that plays out the opposite of how we mere mortals expect is an irony to the audience watching from above.
• Sometimes, the type of irony above is created deliberately. An “ironic punishment” is one designed to perfectly fit the crime. This could mean giving them exactly what they want until they’re sick of it. It could mean showing someone spoiled and ungrateful what real hardship means, or treating someone exactly how they treated others.
• Dictionaries now think the most common use is, “the use of words to express something other than and especially the opposite of the literal meaning.” This isn’t exclusively used of words; It’s common for visual media to use images to, for example, show the villains as being just like the Nazis, and sometimes, even composers of instrumental music get into the game, reversing musical conventions.
• From there, it’s extended further to “a sardonic style of humor” that shades into sarcasm or simple mockery.
• More loosely, the word is now commonly used to mean anything unexpected, especially if it’s amusing or frustrating, such as “rain on your wedding day,” “a black fly in your chardonnay,” “a traffic jam when you’re already late,” or “ten thousand spoons when all you need is a knife.”
• Finally, there’s a little-used sense of the word called “Socratic irony,” which mainly involves asking another person to justify absolutely everything by disingenuously pretending to always need another explanation or clarification. When Plato writes both sides of the conversation, this always ends up exposing some contradiction at a more basic level.