Example:
I am a rock.
do not use like or as in the sentence
http://library.thinkquest.org/J0112392/metaphor.html
http://www.rhlschool.com/eng3n26.htm
http://knowgramming.com/election_metaphors.htm
http://www.tnellen.com/cybereng/lit_terms/metaphor.html
http://owl.english.purdue.edu/handouts/general/gl_metaphor.html
http://www.sil.org/linguistics/GlossaryOfLinguisticTerms/WhatIsAMetaphor.htm
http://www.teachervision.fen.com/poetry/literary-techniques/5453.html
http://missrumphiuseffect.blogspot.com/2008/02/monday-poetry-stretch-metaphor-poems.html
http://www.tnellen.com/cybereng/lit_terms/metaphor.html