We’ve all seen (or experienced) a doctor gently tapping on the chest or stomach during a check up and wondered, “What exactly are they listening for?” or “How does tapping help diagnose anything?”

This centuries old method is called percussion, and surprisingly, it works a lot like tap testing in engineering and manufacturing. Just as engineers tap materials like fibreglass, carbon fibre, or metal to find hidden flaws, doctors tap the human body to detect what’s going on beneath the surface. Each tap creates a sound that tells a different story.

It's important to note, in medicine, percussion is just a quick first check. It helps the doctor listen for anything that might sound unusual. If everything sounds normal, more tests usually aren’t needed. But if something seems off, then tests like X-rays, CT scans, or ultrasounds are used to look closer.

The Chest

When a doctor taps on your chest or back, they’re listening to how your lungs respond. Healthy, air-filled lungs make a clear, resonant sound, almost like a hollow drum (Physio-pedia). A dull sound points to something denser, such as fluid or an infection(Stanford Medicine). A loud, booming, hyper-resonant sound usually means too much air is trapped. In short, your chest works like a drum, and the note changes depending on what’s inside.

The Belly

The abdomen has its own rhythm. A tap over the intestines usually makes a drum like sound called tympany, caused by gas inside (JoVE). A dull sound instead may reveal the solid presence of the liver or spleen, or fluid build-up in the abdomen. Doctors sometimes use a technique called “shifting dullness,” where the sound moves as fluid sinks and gas rises when a patient changes position (NCBI). It’s a remarkably simple way to map what’s happening inside the gut.

The Forehead or Cheeks

Sinuses can also be checked with a tap. When a doctor gently strikes your forehead or cheekbones, they’re looking for tenderness or a subtle change in sound. Healthy, air-filled sinuses sound lighter, while mucus-filled ones produce a duller note.

The Knees

Not all taps are about sound. When your doctor taps just below the kneecap, they’re checking your patellar reflex. If your leg kicks forward, it shows the reflex arc between tendon and spinal cord is intact. This isn’t percussion, it’s about movement. But it proves how even a simple tap can reveal a lot of information.

Why it’s so important

What’s remarkable is how much doctors can learn from such a simple technique. With no machines, no X-rays, and no ultrasounds, these taps give fast, reliable clues about what’s happening inside the body. It’s the same in engineering: a quick tap on a structure can expose hidden weaknesses invisible to the eye.

At RESONIKS…

We apply this same principle of percussion in manufacturing, but with modern technology. Instead of a stethoscope, our AI-powered acoustic system taps and listens to materials like metal, carbon fibre, and composites. Subtle changes in sound reveal cracks, weak bonding, or hidden flaws that traditional inspection methods might miss.

It’s faster, safer, and more accurate quality checks that ensure every component meets the highest standards, whether it’s used in cars or aircraft. Because in both medicine and manufacturing, the smallest sounds often reveal the biggest problems.