The zombies are fiction. The science isn't.
Every part turns on something real. Here it is in plain English, with sources. Not medical advice.
SEEN IN PART 1Is there a real virus that spreads through a bite?
Rabies spreads through saliva, usually by a bite or a scratch, and attacks the central nervous system. Its "furious" form brings hyperactivity, excitable behavior and hallucinations. Unlike the story, it's slow: incubation is typically 2 to 3 months, and can be anywhere from one week to one year. Rabies is vaccine-preventable, but once symptoms appear it is virtually 100% fatal.
SEEN IN PART 1Can something take over a body but leave the brain alone?
In ants, yes. The fungus Ophiocordyceps unilateralis invades a tropical carpenter ant's whole body and steers it until it dies clasped to the underside of a leaf or twig. Then spores bloom from its head and drift to the ground below. The eerie part: researchers found the fungus works the ant's muscles while leaving its brain untouched.
Source: National Geographic: See What's Controlling These Zombie Ants (2017) ↗
SEEN IN PART 1Why can't the smartwatch find a heartbeat?
It reads your pulse with light, a method called photoplethysmography. Blood absorbs green light, so Apple Watch, for example, flashes green LEDs hundreds of times per second while light-sensitive photodiodes measure how much your wrist absorbs. Each heartbeat pushes more blood through and absorption rises, then it drops between beats. No blood moving, no rhythm to find.
Source: Apple Support: Monitor your heart rate with Apple Watch ↗
SEEN IN PART 2Can you hurt an ankle and feel nothing?
Some people really can. In channelopathy-associated congenital insensitivity to pain, a rare inherited condition caused by changes in the SCN9A gene, people never feel pain when they're injured, from birth on. Without that alarm, they often end up with wounds, bruises and broken bones, and long-lasting joint injuries can lead to deformities. Pain is the warning that tells you to stop.
Source: MedlinePlus Genetics (NIH): Congenital insensitivity to pain ↗
SEEN IN PART 2Can people really smell fear?
There's evidence they can. In a 2012 study in Psychological Science, researchers collected sweat from men while they watched a frightening film. Women who then smelled the "fear sweat" made fearful facial expressions themselves, and their sniffing and eye scanning changed too. The kicker: they weren't aware of any of it.
Source: Association for Psychological Science: The Knowing Nose (de Groot et al., 2012) ↗
SEEN IN PART 3Can your body start eating before you take a bite?
Yes. Scientists call it the cephalic phase: the sight, smell and taste of food trigger saliva and stomach secretions before any nutrients are absorbed. In people, even seeing food sealed in a plastic container sets it off, and adding smell and taste makes the response stronger. These reflexes are linked to the motivation to eat.
Source: Appetite: Power & Schulkin, Cephalic phase responses (2008) ↗
SEEN IN PART 4Does blood really have a smell?
Yes, and a key part of it is one molecule: trans-4,5-epoxy-(E)-2-decenal, or E2D. Humans can detect it at just 0.078 to 0.33 parts per trillion. In a 2017 study, wolves reacted to E2D about as strongly as to real blood, while people who smelled it leaned back and showed higher physiological arousal. To a predator it means food; to us, danger.
Source: Scientific Reports: Arshamian et al., A mammalian blood odor component (2017) ↗
SEEN IN PART 4Should Theo's hoodie even have a drawstring?
Probably not. U.S. safety regulators treat hood and neck drawstrings on children's upper outerwear in sizes 2T to 12 as a "substantial product hazard," because they can snag and strangle. CPSC staff know of 26 deaths and 73 nonfatal incidents tied to them between January 1985 and June 2019, most often on playground slides. Theo found a better use for his.
Source: U.S. CPSC: Drawstrings in Children's Upper Outerwear ↗
SEEN IN PART 4What is 147.30 on a radio?
A frequency: 147.30 megahertz. It sits inside amateur (ham) radio's 2-meter band, which runs from 144 to 148 MHz. On the ARRL band plan, 147.00 to 147.39 MHz is set aside for repeater outputs, the channels that relay stations transmit on. In other words, it's ham radio, not a random walkie-talkie channel.
Source: ARRL, the national association for amateur radio: Band Plan ↗