1.) The estrous cycle is also known as when an animal is "in heat":

Estrus is derived via Latin oestrus (frenzy, gadfly), from Greek οιστρος (gadfly, breeze, sting, mad impulse). Specifically, this refers to the gadfly that Hera sent to torment Io, who had been won in her heifer form by Zeus. Euripides used "oestrus" to indicate "frenzy", and to describe madness. Homer uses the word to describe panic [footnote: of the suitors in Odyssey book 22]. Plato also uses it to refer to an irrational drive and to describe the soul "driven and drawn by the gadfly of desire". Somewhat more closely aligned to current meaning and usage of "estrus", Herodotus (Histories ch.93.1) uses oistros to describe the desire of fish to spawn.

The earliest use in English is of "frenzied passion". In 1900 it was first used to describe "rut in animals, heat".

from http://en.wikipedia.org/wiki/Estrous_cycle#Etymology_and_nomenclature

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