A tatoo inserts a design with ink onto the body with needles
Oh that's interesting! You can also inject medication through needles to the human body! What other functions are there for needles?
Tattoo
A tattoo is a form of body modification where a design is made by inserting ink, dyes and pigments, either indelible or temporary, into the dermis layer of the skin to change the pigment. The art of making tattoos is tattooing. 
Tattoos fall into three broad categories: purely decorative (with no specific meaning); symbolic (with a specific meaning pertinent to the wearer); pictorial (a depiction of a specific person or item). In addition, tattoos can be used for identification such as
. Some cultures create tattooed marks by hand-tapping the ink into the skin using sharpened sticks or animal bones (made into needles) with clay formed disks or, in modern times, actual needles.
The most common method of tattooing in modern times is the electric tattoo machine, which inserts ink into the skin via a single needle or a group of needles that are soldered onto a bar, which is attached to an oscillating unit. The unit rapidly and repeatedly drives the needles in and out of the skin,