The removal of the ovaries together with the Fallopian tubes is called salpingo-oophorectomy. Oophorectomy and salpingo-oophorectomy are not common forms of birth control in humans; more usual is tubal ligation, in which the Fallopian tubes are blocked but the ovaries remain intact.
In humans, oophorectomy is most usually performed together with a hysterectomy - the removal of the uterus. Its use in a hysterectomy when there are no other health problems is somewhat controversial.
In animals, spaying involves an invasive removal of the ovaries, but rarely has major complications; the superstition that it causes weight gain is not based on fact. Spaying is especially important for certain animals that require the ovum to be released at a certain interval (called estrus or "heat"), such as cats and dogs. If the cell is not released during these animal's heat, it can cause severe medical problems that can be averted by spaying or partnering the animal with a male.
The buttocks are the two masses of muscle (gluteus maximus, sometimes abbreviated to "glute") and fat covering the posterior aspect of the human (primate) pelvis. They allow humans (primates) to sit upright comfortably without resting weight on their feet, as (for example) cats and dogs do when they sit upright.
In many cultures, corporal punishment is traditionally delivered on the buttocks (it is then called spanking). This is especially true for lighter punishment and domestic discipline on children (and in some cultures, on wives). Different reasons have been put forward to explain this: