Short answers, pulled from the story.
A sense is a biological system an organism uses for sensation, the process of gathering information about its surroundings by detecting stimuli. Sense organs collect stimuli such as a sound or smell and transduce them into a form the brain can understand.
Although five senses were traditionally identified as sight, smell, touch, taste, and hearing, many more are now recognized. Listing all sensory modalities can reach as many as 17, and human absolute thresholds have been tabulated for between nine and 21 external senses.
By function, the receptor cell types are mechanoreceptors, photoreceptors, chemoreceptors including osmoreceptors, thermoreceptors, electroreceptors, and nociceptors. Mechanoreceptors read pressure, vibration, sound, and balance, photoreceptors convert light, chemoreceptors interpret taste and smell, thermoreceptors sense heat or cold, and nociceptors register tissue damage.
The absolute threshold is the minimum amount of stimulation needed to detect a stimulus 50 percent of the time. Tabulated examples include detecting a candle flame 48 kilometers away on a dark clear night and a teaspoon of sugar in 7.5 liters of water.
Some animals can detect electric and magnetic fields, infrared light, air moisture, or polarized light, and others perceive through echolocation. Pit vipers sense prey body heat through infrared, birds navigate by magnetoception, and the platypus has the most acute electroception among mammals.
Interoception is any sense normally stimulated from within the body, relying on sensory receptors in internal organs and tissues. It includes hunger, thirst, the perception of suffocation, blood pressure sensing by baroreceptors, and cardioception, the perception of the heart's activity.