In pictures: US candidates' body language

New York Senator Hillary Clinton, meanwhile, can appear unfeminine, for example, by talking in a low voice, the body language expert says.

"She also 'steeples' [joining the fingertips of both hands] when she talks, an unusual gesture for women and more of a 'male' power signal, with phallic connotations," Ms Wood adds.

She believes the former first lady was genuine when she appeared to choke back tears while addressing voters just before winning New Hampshire's primary.