Everyone who has squeezed an old bath duck and watched black specks come out has asked this. The answer is simple and slightly grim.

What is happening

A squeaking duck has a hole in its base. Under water, squeezing the duck expels air and then draws water back in through that hole.

That water does not fully drain. It sits inside a warm, dark, enclosed space that never dries out, which is close to ideal conditions for mould. The black specks are mould colonies breaking loose.

Why cleaning does not really solve it

You can flush a duck with hot water and a little vinegar or bleach solution, squeeze it out and dry it hole-down, and that helps.

But you cannot see inside, you cannot scrub inside, and the hole will let water back in the next time it is used. It is management rather than a fix.

The actual fix

A fully sealed duck with no hole at all. Nothing goes in, so nothing grows. It cannot squeak and it cannot squirt, and that is the entire trade.

For any shared setting — a pool, a nursery, a clinic play area — sealed is usually the only answer that survives an infection-control conversation.

If you must have the squeak

Buy sealed for the shared settings and squeaking for home, rinse and dry hole-down after use, and replace them rather than keeping them for years.

And plug the hole with a dab of hot glue if you want to keep a favourite duck — it kills the squeak and stops the problem.