Yes, a sword can rust if it is dropped in a washing machine and exposed to moisture for an extended period of time. Swords are typically made of metal, and most metals, including the ones commonly used in swords like steel, can rust when exposed to water and oxygen.
A washing machine is a moist and humid environment, and if the sword remains in there for a considerable amount of time, the moisture can lead to the formation of rust on the metal surface. Rust is a chemical reaction that occurs when iron or steel reacts with oxygen and water, forming iron oxide. Over time, rust can deteriorate the metal, leading to corrosion and potentially damaging the sword.
To prevent rusting, it's essential to keep the sword dry and store it in a cool and dry place, preferably with some protective coating or oil to inhibit moisture exposure. If a sword accidentally gets wet, it should be thoroughly dried and lightly oiled to prevent rust formation.