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Health and the body2–3 minAround a typical joint, tendons transmit a muscle's pull to bone while ligaments connect bones and help stabilize them. Similar-looking connective tissues therefore contribute to movement in different ways.

Health and the body3–7 minA study can measure an average benefit without deciding what matters most to a particular patient. The relevance of the evidence, possible harms and the person’s goals all affect a decision made with a clinician.

Health and the body5–7 minA brain scan is a map, but surgery needs that map to line up with a real patient in a real position. Navigation systems register the two using matching features or markers, then relate tracked instruments to the images. Even a good initial match has limits: anatomy can shift during an operation, so the original map may need updating.

Health and the body3–7 minFive seconds sounds like a convenient boundary between clean and contaminated. A laboratory study instead tested several contact times, foods, and surfaces, finding that time was only one part of the transfer process. The useful distinction is between how many bacteria move onto food and whether someone subsequently becomes ill; this experiment measured the former.

Health and the body5–7 minFood and air travel through a shared region of the throat, but they need different destinations. Swallowing coordinates movements that carry food toward the esophagus while protecting the airway. The transition from moving food around the mouth to the largely automatic sequence below it involves several muscles and nerves working together.

Health and the body3–5 minA breath-hold diver carries oxygen in more places than the lungs. Blood hemoglobin and muscle myoglobin also hold oxygen, while changes in heart rate and blood flow affect how those stores are used. The oxygen supply remains finite throughout the dive.

Health and the body3–7 minYou may hear that a sung note is wrong and still struggle to produce the right one yourself. Listening and singing require different operations: detecting a pitch, remembering it, and translating it into a vocal action. Experiments on pitch imitation suggest that difficulties in those steps need not occur together.

Health and the body5–7 minShowing that a medicine changes an outcome and explaining every step of how it works are different research tasks. Paracetamol offers a case for exploring that distinction. Evidence from patients, laboratory experiments, and proposed biological pathways answers different questions, so an uncertain mechanism does not make every explanation equally plausible.

Health and the body3–5 minYou can lie completely still while your cells keep spending energy. One quiet expense is maintaining the difference between the sodium and potassium concentrations inside and outside a cell, using a pump powered by ATP.

Health and the body3–7 minA memorable accident and a continuing burden of air pollution are difficult to compare by intuition alone. One approach estimates deaths for the same amount of electricity, including defined stages of the supply chain. The answer still depends on the geography, time period, harms counted, and uncertainty in the estimates.

Health and the body3–7 minFeeling better after a placebo is an observation. Showing that the placebo caused the improvement requires a comparison, because symptoms can change with time and people can report them differently. The distinction matters whenever a treatment’s effects are being measured.

Health and the body4–5 minTurning your head and tilting it provide different challenges for your balance system. Semicircular canals help signal rotation, while the otolith organs respond to gravity and linear motion. The brain combines this information with signals from vision and the rest of the body.