Mice are encountered during the Grim Tales quest while the player is shrunk. The mouse's drops look large when viewed on the floor, but they appear normal-size inside a player's inventory. Picking up and re-dropping large drops yields normal sized drops. Presumably, the mouse is as large as a rat if the player were normal-sized (such as the ones found around Lumbridge) but has a higher combat level because the player is smaller.
These mice cannot be chased as vermin by a cat.
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