What your body's noises say about you

Most sounds from your body are perfectly normal, if slightly embarrassing. But they can also suggest medical issues that need investigation. TANITH CAREY reveals why they happen... and what they could mean

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These odd, unpredictable noises can often take us by surprise - and be annoying because it feels like we have no control over them. They start when your diaphragm - the thin sheet of muscle under the rib cage that rises and falls to help our lungs expand and contract - goes into a spasm.

The hic sound is made when the diaphragm forces up your chest and snaps your vocal cords shut as you breathe out.

Your diaphragm is controlled by two large bundles of nerves, called the phrenic nerves.

These send messages from your brain through to the lower part of your abdomen. If your stomach gets bloated from drinking lots of fizzy drinks or eating too much too quickly, the pressure can irritate these nerves, triggering contractions of your diaphragm. Pharmacist George Sandhu, of Well Pharmacy, one of the UK's largest pharmacy chains, says: "Most hiccups are harmless and settle within a few minutes to a couple of hours.

"You should seek advice if they are persistent, like lasting more than 48 hours. Anything beyond that isn't normal and should be checked. If they keep coming back, it could point to irritation of the stomach or oesophagus or perhaps the nerves controlling the diaphragm."

The reason knuckles crack is that the space where your joints and bones meet is a capsule full of slippery egg-white like material. This is synovial fluid which helps the bone ends glide past each other. Inside this fluid is a range of dissolved gases, like nitrogen, oxygen and carbon dioxide.

When you stretch your finger joints back further than they normally go, for example by pushing your fingers backwards, the space between these bones gets bigger. The opening up of this space creates a vacuum that pulls these gases out of the fluid in the same way as opening a bottle of fizzy water brings bubbles to the surface.