The smallest object a human eye can see in special condition is 0.116 mm.
Virus
According to Quantum Theory, if light consists of a photon then photon will be the smallest particle to which human can observed because human eye can see any thing if a light rays get reflected from any object or matter
It means that the detail of the object or the object itself cannot be seen without the aid of a microscope. The smallest object that a human eye can see is 50 microns. Smaller than that is microscopic.
The smallest bone in the human body is the stapes (or stirrup) in the ear.
the human cell
Bacteria
The violin is said to be the most diversely expressive instrument, second only to the human voice.
The malleus, the incus, and the stapes are the three smallest bones in the human body and they are all in the ear.
The smallest human bone is the stapes (aka stirrup) which is one of the three auditory ossicles of the middle ear.
The smallest brain weighed only 24 pounds.
The smallest facial bone is known as the lacrimal bone.
The smallest is the sperm cell, the largest the ovum