In his work on the two-point threshold, weber found that the most sensitive area (smallest threshold) was the and the least sensitive area (largest threshold) was the

tongue; middle of the back

Explanation:

In physiology, the two-point threshold means that there must exist a threshold distance, above which any given subject can differentiate between two different sensations. In physics, the two-point threshold is the smallest distance that exists between two points where the person can distinguish those two points as distinct and not one. This two-point threshold work by Weber found that the most sensitive area where the threshold distance was the smallest was the tongue and the least sensitive area where the distance was largest was the middle of the back.

The answer would be sand and gravel

Hunting in the darksome fish rely on senses beyond sight. in the darkness of the marianas trench, a fish called the rattail has an extremely sensitive sense of smell. the fish uses scent, rather than sight, to steer toward food. once it's near food, the rattail uses a special organ on the bottom of its chin to guide itself by feel.marine snowone staple of the deep sea diet is "marine snow," flakes of organic, edible substances that sink down from the upper ocean. animals at the ocean's bottom find sustenance in everything from the bodies of dead creatures to fecal matter. marine snow is diverse enough to support numerous species. for instance, several species of snails and worms feed exclusively on deceased whales.microorganismsthe deep sea is an intricate ecosystem, and even the ocean floor itself plays a part. hydrothermal vents are cracks in the sea floor where erupting magma mixes with ocean water to produce plumes of hot, sulfur-rich chemicals. some microbes can use these chemicals for energy, sustaining their existence and that of the animals who depend on their roles in the deep sea food chain.