contortionist

from WordNet (r) 3.0 (2006)

contortionist
    n 1: an acrobat able to twist into unusual positions

from The Collaborative International Dictionary of English v.0.48

Contortionist \Con*tor"tion*ist\ (k[o^]n*t[^o]"sh[u^]n*[i^]st),
   n.
   One who makes or practices contortions; especially, a gymnast
   who is able to twist the limbs into positions impossible for
   normal people to achieve.
   [1913 Webster +PJC]