How does the platypus detect prey with its bill?

The answer

The platypus bill contains around 40,000 electroreceptors and 60,000 mechanoreceptors arranged in characteristic stripes, forming one of the most sensitive electroreception systems in any mammal. When prey such as shrimp or insect larvae move their muscles or flick their tails, they generate tiny electrical fields that the platypus detects while swimming with its eyes, ears, and nostrils sealed shut. The brain processes the time difference between electrical and mechanical signals to calculate the precise distance to the prey. The platypus is one of only two groups of mammals known to possess electroreception, the other being echidnas.