An animated object is a mundane item enchanted to a semblance of life through powerful magic. These can literally be anything, from a weapon, to a set of candlesticks. It is entirely up to the whim of its enchanter what its base object is. Those skilled in crafting constructs can make such life-like creatures last indefinitely so long as they are not destroyed or the magic bringing them to “life” is not dispelled.
Sometimes the shape of an animated object makes it more effective than it would otherwise be. It might be made of metal and therefor more resilient to attack, or it might have wheels that make it go faster, or be small and sharp so it can attack more precisely. Generally such attributes are fairly easy to recognize, though subtle dissimilarities can be the difference between charming antics and a deadly trap.