An often raised question is that about the
oval curve
that describes an egg.
Above formula gives, for certain values for the parameter a, a rather good
presentation of an egg. I call the curve the egg curve or the Wassenaar
(egg) curve.
Starting with an ellipse, with proper measures, make one end smaller than the
other one.
This leads ^{1) }to a quartic function.
When
taking linear transformation into account, parameters b (roundness) and c
(difference between the ends) vanish into one parameter a (b/c) in above
equation. A good chicken egg has a value for parameter a between 5 and 6.
Other curves that can be used as an approximation of an egg are:
Ken Sasaki wrote a paper for the American Journal of Physics about the
spinning possibilities of several eggshaped forms ^{2)}.
notes
1) Via y = ± √(1  bx^{2}) + c x^{2}
2) The paper is named: 'Spinning eggs  which end will rise?'.
