Mmmm... it is not an easy thing to select one favourite. However, I've already been very fond of this one, by Canadian writer Margaret Atwood.

She considers evading him

I can change my-
self more easily
than I can change you

I could grow bark and
become a shrub

or switch back in time
to the woman image left
in cave rubble, the drowned
stomach bulbed with fertility,
face a tiny bead, a
lump, queen of the termites

or (better) speed myself up,
disguise myself in the knuckles
and purple-veined veils of old ladies,
become arthritic and genteel

or one twist further
collapse across your
bed clutching my heart
and pull the nostalgic sheet up over
my waxed farewell smile

which would be inconvenient
but final.
"We do maths with our brain but we must teach it with our heart"
Claudi Alsina, Department of Mathematics, UPC (Spain)