http://en.wikipedia.org/wiki/Trefoil_knot
In[1]:= ParametricPlot3D[{Sin[t] + 2 Sin[2 t], Cos[t] - 2 Cos[2 t], -Sin[3 t]}, {t, 0, 2 Pi}]
Out[1]= ...PlotSnipped...
http://en.wikipedia.org/wiki/Figure-eight_knot_(mathematics)
In[3]:= ParametricPlot3D[{(2 + Cos[2 t]) Cos[3 t], (2 + Cos[2 t]) Sin[3 t], Sin[4 t]}, {t, 0, 2 Pi}]
Out[3]= ...PlotSnipped...
After you display the plots you can position the mouse inside the plot box, press the left mouse button and drag to change the orientation to better understand the structure.
