What is a unique characteristic of an electric blasting cap?

An electric blasting cap is designed to be initiated by the flow of electrical current, which is why it has wires coming out of it. These wires are essential for connecting the blasting cap to a power source, such as a battery or detonator switch, allowing for precise control over the detonation process. This method of ignition offers greater safety and reliability compared to non-electric blasting methods, as it minimizes the risk of accidental ignition and allows for remote detonation.

The other choices do not accurately describe the defining feature of an electric blasting cap. While some blasting caps may contain black powder or be waterproof, these characteristics are not unique to electric caps. Additionally, the use of a time fuse is associated with non-electric blasting caps, making this characteristic irrelevant in the context of electric blasting caps.