Short answers, pulled from the story.
The absolute threshold is the precise minimum amount of stimulation required for detection fifty percent of the time. A single photon of light can trigger a visual signal, and a drop of perfume can be detected in a volume the size of three rooms. Hearing thresholds allow detection of fluid movement in the semicircular canals within a range of about twenty to twenty thousand hertz.
Sound waves travel from the auricle to the tympanic membrane and are transmitted by three tiny bones known as the ossicles. The malleus, incus, and stapes translate to hammer, anvil, and stirrup to transmit vibrations to the inner ear. Hair-like fibers detect mechanical motion within a range of about twenty to twenty thousand hertz and fire neurons in the auditory cortex.
The perception of flavor is a complex deception that relies on the integration of taste and smell. The olfactory system has three hundred eighty-eight functional receptors that detect airborne molecules dissolving into the mucus lining the nasal cavity. The loss of the sense of smell can result in food tasting bland and lead to a general sense of despair and even mild depression in some individuals.
The platypus possesses the most acute sense of electroception among mammals and uses electroreceptors in vibrissal crypts on its snout. It detects electric fields as weak as four point six microvolts per centimeter to locate prey from the seafloor. Sharks use the ampullae of Lorenzini to sense changes in electric fields in their immediate vicinity.
Interoception is a hidden internal landscape of sensation that detects stimuli from internal organs and tissues to maintain homeostasis. It includes the perception of hunger, thirst, suffocation, and nausea, as well as the detection of blood pressure and carbon dioxide levels. The absence or impairment of this internal sense can lead to clinical conditions such as alexithymia where individuals struggle to identify and describe their emotions.