Weapon/object duality is a game concept that is a feature, often mistaken as a glitch, in Problem Sleuth whereby all weapons have an innocuous double, switching back and forth between the two forms seemingly at random. Interestingly, the object and the weapon may have large differences in their degree of encumbrance. Bizarrely, they often do not, the hairpin being heavy enough to break the glass in the skylight. Pumpkins also seem to have this effect in Jailbreak, though their innocuous double is nothing (or air).
Originally, the effect would be triggered whenever the object was named (You would have a Gun if you called it a Key, and vice-versa). This later changed to whatever was funnier at the moment.
In Homestuck, the Midnight Crew exhibits this with their decks of cards. Every card in their deck corresponds to an object, usually (but not always) a weapon, with the deck as a whole corresponding to a storage unit that stores each individual object.
Kanaya Maryam has a Chainsaw/Lipstick, but it appears to collapse or expand mechanically from one object into the other. This oddly achieves the same effect as the duality seen in Problem Sleuth without any "glitch"/special mechanic occurring. Her chainsaw/lipstick appears to be designed to transform rather than doing so for no apparent reason such as in Problem Sleuth and the Midnight Crew's cards.
Lord English's staff switching to an assault rifle.
Later on in Homestuck: Intermission 2 it's revealed that Lord English's CAIRO OVERCOAT turns into an Egyptian Sarcophagus, which is a play on gangster slang for coffin: "Chicago Overcoat".
After the scratch in Homestuck, Jane Crocker also owns a spoon that on 11/11/11 11:11 switches into a fork, and from then on is able to switch between the spoon and the fork.
Calliope has a white wand
that is the innocuous double of her magnum. She notes that Caliborn has a similar but more heavy-handed weapon, which later turns out to be a scepter/assault rifle.