Hidden hand placed (always there) interactive sneaky odd rocks, dusty bookshelves , bloody planks, chains, dusty piles etc. that have no real stand out from environment yet they would be a chance to be movable and a chance to be a dud, if movable there is a chance to drop a upgrade or maybe runes/ gems/gear. These do not light up when hoving your mouse over them, and can only be noticed once clicked and moved. Can drop all tiers of loot.
This effect would make the environment feel more interactive and alive, make you pay attention to environment and want to explore the details.