A short circuit (or short) is an electrical circuit that allows a current to travel along an unintended path with no or a very low electrical impedance.
It is an abnormal connection between two nodes of an electric circuit that is intended to be at different voltages. This results in an electric current limited only by the equivalent resistance of the rest of the network which can cause circuit damage, overheating, fire or explosion.
A common type of short circuit occurs when the positive and negative terminals of a battery are connected with a low-resistance conductor, like a wire. With a low resistance in the connection, a high current will flow, causing the delivery of a large amount of energy in a short period of time.
A high current flowing through a battery can cause a rapid increase of temperature, potentially resulting in an explosion with the release of hydrogen gas and electrolyte (an acid or a base), which can burn tissue and cause blindness or even death. Overloaded wires will also overheat causing damage to the wire's insulation, or starting a fire.
In electrical devices unintentional short circuits are usually caused when a wire's insulation breaks down, or when another conducting material is introduced, allowing charge to flow along a different path than the one intended.
A short circuit may lead to formation of an electric arc. The arc, a channel of hot ionized plasma, is highly conductive and can persist even after significant amounts of original material from the conductors has evaporated. Surface erosion is a typical sign of electric arc damage. Even short arcs can remove significant amounts of material from the electrodes. The temperature of the resulting electrical arc is very high (tens of thousands of degrees Fahrenheit), causing the metal on the contact surfaces to melt, pool and migrate with the current, as well as to escape into the air as fine particulate matter.
The entire motherboard has electronic components, ranging from capacitors, resistors, IC chips and the like. The moment you turn on your computer energy runs through out the components and motherboard. Dropping a metal wire or metal twist ties could in fact divert energy from one point to another damaging your GPU, CPU, or other components on your mother board.