You're probably familiar with South Korea's glow-in-the-dark cats (if not, here's a video). They're genetically modified cats with fluorescent pigmentation in their skin that causes them to glow red under UV light. The researchers then cloned them, successfully carrying the fluorescent gene to the next generation of kitty clones. For better or for worse, it looks like genetic engineering is here to stay, which begs the question: How will we know when we've gone too far? What's the line between scientific progress and irreversibly changing the DNA of a life form?

If that sounds extreme, just check out these 10 insane cases of genetic engineering.

10 Spider Goats

Spider silk has approximately a million and a half uses, and we're finding more every day. Due to its incredible strength in relation to size, it's been researched for use in bulletproof vests, artificial tendons, bandages, even computer chips and fiber optic cables for surgery. But harvesting enough silk requires tens of thousands of spiders and a lot of waiting time, not to mention the fact that spiders tend to kill other spiders in their territory, so you can't farm them like, say, bees.

So researchers are turning to goats, the only animal in the world that could possibly improve by having more spider DNA. Professor Randy Lewis, of the University of Wyoming, has isolated the genes that produce dragline silk, the strongest type of silk spiders use when they anchor their webs (most spiders produce six different types of silk). Then he spliced the genes with the genes used by goats to produce milk, mated that goat, and confirmed that three of the seven baby goats retained the silk-producing gene.

All that's left to do now is milk the goats and filter out the spider silk, maybe fight a little crime on the side. And Prof. Lewis isn't immune to irony—his office is covered with Spiderman posters.

9 Singing Mice

Most of the time, scientists go into an experiment with a purpose. Sometimes, however, they just throw a bunch of genes into a mouse and wait to see what happens. That's how we got this mouse that chirps like a bird. It's part of the Evolved Mouse Project, a Japanese research project that's taking a brute force approach to genetic engineering—they're modifying mice, letting them breed, and just sort of noting down the results.

While checking a new litter of mice one morning, they discovered one of the baby mice "singing like a bird." Excited, they focused on that mouse and now have over 100 mice that can sing, and they noticed something else interesting—when regular mice grew up around singing mice, they began to use different sounds and tones, sort of like a dialect spreading through a human population. Here's a video of one of the mice.

What will the singing mice be used for? Who knows. But the project's goal is to artificially speed up evolution, and it seems to be taking some unexpected directions at the very least. Professor Takeshi Yagi also claims that they have a mouse with "short limbs and a tail like a dachshund." Strange.


8 Super Salmon

This example is probably going to appear in US supermarkets pretty soon: Genetically modified Atlantic salmon, engineered to grow twice as large and twice as fast as regular salmon. Created by AquaBounty and dubbed the "AquaAdvantage salmon," it has two specific gene alterations: The first is a gene from Chinook salmon, which isn't used for food as widely as the Atlantic salmon, but which grows much faster at a young age.

The second is a gene from an eelpout, a bottom-dwelling eel-like fish that continually grows all year round—salmon, on the other hand, typically only grow during the summer. The result is a perennial super-growing salmon, and it's on the fast track to becoming the first genetically engineered animal approved for human consumption. That is to say, the FDA already gave its approval, in December 2012.

7 Viral Bananas

In 2007, an Indian research team published their research for creating a strain of bananas that inoculates people against Hepatitis B. The team also successfully altered carrots, lettuce, potatoes, and tobacco to carry the vaccine, but feel that bananas are the most reliable transport system.

To summarize the way vaccines work, a weakened version of the virus or germ is injected into the person. It's not strong enough to make you sick, but it's just enough to kick your body's production of antibodies into effect, therefore protecting you in case the full-strength version of the virus tries to enter your system.

But there are plenty of ways vaccinations can go wrong, from allergic reactions to just plain not working. And why is it recommended that you get a flu shot every year? Because viruses adapt in response to the vaccine—