"What Is A Kiss?" joke

Prof. of Algebra: kiss is two divided by nothing.
Prof. of Geometry: kiss is the shortest distance between two straight lines.
Prof. of Physics: kiss is the contraction of mouth due to the expansion of the heart.
Prof. of Chemistry: kiss is the reaction of the interaction between two hearts.
Prof. of Zoology: kiss is the interchange of unisexual salivary bacteria.
Prof. of Physiology: kiss is the juxtaposition of two orbicularis oris muscles in the state of contraction.
Prof. of Dentistry: kiss is infectious and antiseptic.
Prof. of Accountancy: kiss is a credit because it is profitable when returned.
Prof. of Economics: kiss is that thing for which the demand is higher than the supply.
Prof. of Statistics: kiss is an event whose probability depends on the vital statistics of 36-24-36.
Prof. of Philosophy: kiss is the persecution for the child, ecstasy for the youth and homage for the old.
Prof. of English: kiss is a noun that is used as a conjunction; it is more common than proper; it is spoken in the plural and it is applicable to all
Prof. of Engineering: What is a kiss?