Final answer:
Horses tearing down an electric fence when the battery fails is not scientifically documented, but animals like sharks and the platypus can detect electric fields, and electric eels can produce them using electroplaques.
Step-by-step explanation:
The statement that horses will learn to check an electric fence daily with the hairs on their upper lip and then tear it down when the battery fails is not directly supported by scientific evidence regarding animals as electrical detectors. However, it is known that various animals can detect electric fields. For example, sharks can sense electric fields in their snouts as small as 100 mV, and the Australian platypus can detect fields of 30 mV. Electric eels generate their own electric fields through electroplaques to stun prey or defend against predators. This ability to detect or produce electric fields is due to the movement of ions across the cell membrane, resulting in depolarization and repolarization which ultimately produces a nerve signal. In some cases, like the platypus, this ability is crucial for hunting, as they rely on it to detect prey since they are effectively blind underwater.