Donald Trump Jr. tried to make a political point about refugees on Twitter on Sept. 19, but he got it all wrong. The Fix's Philip Bump explains how. (Peter Stevenson/The Washington Post)

This tweet, from Donald Trump's son Donald Jr., makes a good point. Except for the part in blue, which is completely wrong.

If there were a bowl of delicious fruitish-flavored Skittles in front of you and three would kill you, you should not pick up a handful and start eating. That would be a very, very bad idea.

This idea easily scales downward. If you had a carton of eggs and three of the eggs were poisonous, you should absolutely not eat from that carton. If I give you three cookies and all three are poisonous, again: Avoid! I am actively trying to kill you for some reason, perhaps because you are bad at math.

The problem for Donald J. Trump, Jr. is that scaling it the other way doesn't work as well — and that's why the part in blue doesn't apply.

So let's figure out what the analogy is. The libertarian (and Koch brothers-backed) think tank Cato Institute published a report last week assessing the risk posed by refugees. That report stated that, each year, the risk to an American of being killed by a refugee in a terror attack is 1 in 3.64 billion, as Huffington Post's Elise Foley noted on Twitter. From the report:

From 1975 through 2015, the annual chance that an American would be murdered in a terrorist attack carried out by a foreign-born terrorist was 1 in 3,609,709. Foreigners on the Visa Waiver Program (VWP) killed zero Americans in terrorist attacks, whereas those on other tourist visas killed 1 in 3.9 million a year. The chance that an American would be killed in a terrorist attack committed by a refugee was 1 in 3.64 billion a year.

In other words, for every 10.92 billion years that Americans live — one Skittle, if you will — refugees will kill an American in a terror attack in three.

An actual Skittle is about 1 centimeter squared by about a half a centimeter tall (or thereabouts). Setting aside questions of stacking the oblong Skittles in this very large bowl by assuming each will occupy two-thirds of that volume, we're talking about one-and-a-half Olympic swimming pools of Skittles. Wrigley produces 200 million Skittles a day, so this is the entire production line for more than 54 days, transported to an oversized swimming pool and dumped in to the top. And in that pool: Three poison Skittles.

An Olympic sized swimming pool and diving facility are part of a huge swim and gym center in Tunica, Miss. Imagine that the pool is 50 percent longer, and the whole thing is filled with Skittles. (Michael S. Williamson/The Washington Post)

What are the odds you'll pick out one of those three poisoned Skittle in a handful? Let's continue the analogy.

I didn't have any Skittles around, so I grabbed a handful of those terrible mints that old people have and which I also have for some reason. My hand, which is fairly big, held 53 candies. Receipts:

So how many handfuls could I grab before I got one that's poisoned?

Well, it could be one, of course, if the poisoned ones are distributed evenly through the giant pool-and-a-half of Skittles. But the odds say something different. If there is one poisoned Skittle in 3.64 billion, that means I could extract quite a few handfuls before I was likely to pick out a poisoned one.

Specifically, about 68.7 million handfuls. Let's say it takes me one minute to grab a handful and eat them. I would hit a poisoned Skittle, on average, every 130 years. I would also be consuming the equivalent of a package of Skittles every minute, which is about 330,000 calories a day.

As my colleague Aaron Blake notes, there's another layer of complexity. The 200 million Skittles a day that end up in the pool have all passed through Wrigley's stringent quality control system. To continue the analogy in an increasingly awkward way, the United States already screens refugees that arrive in the United States through a multilevel process — the equivalent, I guess, of quality testing Skittles before you take them out of the pool.

The other big problem with Trump's analogy should be obvious by now. We've gone along with it, but depicting refugees fleeing war as inanimate candies is at best disconcerting and at worst offensive. Donald Trump Jr. implies that hundreds of the refugees that have been invited to settle in the United States — refugees who left their homes with their families to escape the threat of the Islamic State or the Syrian regime — are a deadly risk to Americans. That's simply not the case. We can never, no matter how extreme our vetting, ensure that those who enter the country aren't a risk to its residents any more than we can ensure that people born here won't be. Americans born in America commit hundreds of murders a year. In 2014, there were 4.5 murders for every 100,000 Americans. That's a rate thousands of times higher than what's under consideration here.

Trump does have an out, though. If he wants to, he can blame this flawed argument on former congressman Joe Walsh.

Or he can just take out that line in blue. It's still good advice to tell people not to eat poisoned candy, particularly right before Halloween.

During a speech in Phoenix on Aug. 31, Republican presidential candidate Donald Trump talks about what he would as president in response to refugees coming to the U.S. to flee the violence in Syria. (The Washington Post)

Aaron Blake contributed to this report.