The platypus and the echidna are the only mammals that have the power of electroreception, which means they can sense electrical changes. Check out this new Weird Animal Brain to learn how the platypus uses its bill to catch prey underwater!
For more info:
Scheich H., Langner G., Tidemann C., Coles R.B., Guppy A. (1986). Electroreception and electrolocation in platypus. Nature. 319(6052):401-2.
Pettigrew, J.D., Manger, P.R., and Fine, S.L. (1998). The sensory world of the platypus. Philosophical Transactions of the Royal Society B. 353(1372): 1199–1210.
Patel, M. (2007). Platypus Electroreception. Retrieved June 26, 2017, from http://www.reed.edu/biology/professors/srenn/pages/teaching/web_2007/myp_site/index.html