The answer is "Müller-Lyer illusion".
The Müller-Lyer illusion is an optical illusion comprising of an arrangement of lines that end in sharpened stones. The introduction of the sharpened stones influences one's capacity to precisely see the length of the lines. Like most visual and perceptual dreams, the Müller-Lyer illusion enables neuroscientists to ponder the manner in which the cerebrum and visual framework see and translate pictures. Craftsmen have likewise used the hallucination to extraordinary impact in their works.