Eyes are organs of the visual system. They provide animals with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons. [from wikipedia]

Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space.[from wikipedia]

Footprints are the impressions or images left behind by a person walking or running. Hoofprints and pawprints are those left by animals with hooves or paws rather than feet, while "shoeprints" is the specific term for prints made by shoes.[from wikipedia]

Stencil graffiti is a form of graffiti that makes use of stencils made out of paper, cardboard, or other media to create an image or text that is easily reproducible. The desired design is cut out of the selected medium and then the image is transferred to a surface through the use of spray paint or roll-on paint.[from wikipedia]