When females are in heat, they secrete pheromones - chemicals produced by a given species that affect the same species' behavior or physiology. They attract males in the vicinity and help them find a female to mate.
If your pet has unsupervised access to the street, it can easily find a mate and bring home some cute little surprises in 58 to 67 days.
Pheromones were only discovered in 1959, and their concept has changed the way scientists study animals' (and humans'!) behavioral aspects. If you wish to learn more about it, click here: https://www.depts.ttu.edu/animalwelfare/research/pheromones/index.php
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