One thing you need to know to understand this truth.
Exploitation
When two different density media are separated by a semipermeable screen, the lower density molecules move through the semicircles through the higher ones. This process continues until the density of the two is equal. This process is called osmosis.
Example: When some raisins are thrown into the water, after a while it is seen that the raisins have absorbed the water and are slightly swollen.
Leeches have a lot of water in their body. Their bodies are covered by a semi-permeable membrane. When we sprinkle salt on them, they enter the mucus (through which the leech moves). As the concentration of salt outside the body increases, water comes out of their body. When excess water leaves the body, they die as a result of dehydration.