Sodium ions have a single positive charge, and each ion is about five hundred times less effective at shielding than a calcium ion. Suddenly, the negatively charged carbohydrates can feel each other. The result is an explosion of sticky mucus. Last year, Fudge and Gosline found that the vesicles in hagfish mucus also contain a high concentration of positively charged calcium ions. So the same mechanism could be at work in both human and hagfish mucus.
Events are no less violent in the thread cells.
To pack it all into a space just 100 micrometres across, the fibre is coiled into an amazing structure the shape of a rugby ball. But the moment that seawater gets into them, the ends of the tightly coiled thread pop out and the rugby ball begins to unravel. Now things become very messy. Thread cells, mucus and mucin vesicles are all mixed up together. As the ends of the fibres snake out, they get caught in lumps of swelling mucin that surround them.