Here's why a single flying bullet can be so damaging and often deadly

However, for more than 100 years, scientists have toiled to understand why and how guns inflict the damage that they do. Figuring out how to mend such wounds and improve a victim's chances of survival are also critical areas of research, too.

That case could not be more clear for Rep. Steve Scalise of Louisiana and three other people who were shot by 66-year-old James Hodgkinson during practice for a congressional baseball game on Wednesday in Virginia. (Hodgkinson was later killed by Capitol police.)

Though Scalise was not hit in the head or chest, he did receive a particularly complicated wound to his hip. The bullet "travelled across his pelvis, fracturing bones, injuring internal organs, and causing severe bleeding," according to MedStar Washington Hospital Center.

Dr. Jack Sava of MedStar WHC told reporters on Friday that he was feeling "a lot more confident and a lot more optimistic" than just two days ago, but he noted Scalise is still in critical condition and requires a number of additional surgeries.

Bullet wounds can kill a person long after a shooting. In fact, as Lenny Bernstein reported for The Washington Post on Thursday, the pelvis is home to iliac vessels, and "30 percent to 50 percent of injuries to the main iliac vessels result in death".

To humanely probe the physics of gunshot wounds, and ultimately help police solve crimes and doctors save lives, researchers shoot bullets into inert, flesh-like substances. In many cases, they use a large block of gelatin and water to simulate the impact of a speeding bullet on human tissue. Other use glycerin soap.

Here's an example from the YouTube channel EffectiveAffect of what a gunshot simulation in gelatin looks like. This bullet was moving at about 2,900 feet per second through 575 cubic inches of gelatin.

Many factors determine how damaging bullet wounds can be. The type of gun and bullet used, the range of the shot, where on the body a person was shot, and whether or not the bullet exited the body afterward all make a difference.

But some basic principles remain: When a bullet is traveling at lightning-fast speeds, it partially slows down the moment it hits a person. The energy of the blast needs to go somewhere, so it gets radiated outward from the bullet's path to the surrounding tissues. This creates a much larger "mushrooming" effect, which you can see above.

This temporary ballooning of tissue is actually what causes the most damage, according to a post on Mongabay.com. The billowing flesh lacerates blood vessels and surrounding organs, tissues, and bone — and, as Bernstein reports, this shockwave can leave a track of wounding as much as "five to 10 times wider than the bullet."

Gelatin, of course, isn't a perfect proxy for the human body. We have bones and cartilage, which can skew the bullet's path, sending it into a tailspin that could cause it to break apart and get lodged in different spaces, further complicating the severity of the wound.

This why an increasing number of researchers are turning to advanced computer simulations. Such models can recreate the complex layers of tissue in the human body to study a practically infinite number of grievous wounds from all angles, speeds, and styles of bullets (or even shrapnel from mines and improvised explosive devices).

A model that debuted in 2015, for example, simulated a human leg, its skin, muscle, bone, large arteries, and even small veins. Then it applied the physics of fluid dynamics to explore the origins of traumatic blood loss, and the best methods to stop that bleeding.

But as Alex Ossola reported for Popular Science, this and other models aren't perfect — so there's still a lot left for scientists and doctors to learn.

This uncertainty helps explain Scalise is receiving some of the best medical care in the world, but is still in critical (though stable) condition: Gun wounds are as enigmatic as they are damaging and dangerous.

Julia Calderone and David Choi contributed to this post.