a tall blade of grass] with the help of only its skin's general sensitivity to light. The approach of her prey becomes apparent to this blind and deaf bandit only through her sense of smell. The odor of butyric acid, which emanates from the sebaceous follicles of all mammals, works on the tick as a signal that causes her to abandon her post (on top of the blade of grass/bush) and fall blindly downward toward her prey. If she is fortunate enough to fall on something warm (which she perceives by means of an organ sensible to a precise temperature) then she has attained her prey, the warm-blooded animal, and thereafter needs only the help of her sense of touch to find the least hairy spot possible and embed herself up to her head in the cutaneous tissue of her prey. She can now slowly suck up a stream of warm blood." Thus, for the tick, the Umwelt is reduced to only three (biosemiotic) carriers of significance: (1) The odor of butyric acid, which emanates from the sebaceous follicles of all mammals, (2) The temperature of 37 degrees Celsius (corresponding to the blood of all mammals), (3) The hairiness of mammals. Theoretical biology Uexküll anticipated many computer science ideas, particularly in the field of robotics, roughly 25 years before these things were invented. Uexküll views organisms in terms of information processing. He argues every organism has an outer boundary which defines an Umwelt (German word generally meaning "environment", "surrounding world"). Rather than the general meaning, Uexküll's concept draws on the literal meaning of the German word, which is "surround-world", to define the Umwelt as the subjectively perceived surroundings about which information is available to an organism through its senses. This is a subjective Weltanschauung, or "world view", and is therefore fundamentally different from the black box concept, which is derived from the objective Newtonian viewpoint. The organism has sensors that report the state of the Umwelt and effectors that can change parts of the Umwelt. He distinguished the effector as the logical opposite of the sensor, or sense organ. Sensors and effectors are linked in a feedback loop. Sensor input is processed by a Merkorgan and effectors are controlled by a Werkorgan. The modern term "sensorimotor" used in enactive theories of cognition encompasses these concepts. He further distinguishes the Umgebung (that part of the Umwelt that represents distal features of