( Reuters ) - What does Democrat Hillary Clinton's laugh have in common with Republican Rudy Giuliani's cell phone?
Both are causing waves on the U.S. presidential campaign trail for the leading candidates in each party.
For Clinton, her tendency to burst out in a giggle during some public appearances has generated political tongue-wagging.
The New York senator, often seen as an overly serious candidate, has been showing some personality lately.
She laughed at times during questioning on Sunday morning television shows more than a week ago and then hooted with laughter when asked to respond to a critical comment from a rival candidate at a debate last Wednesday in New Hampshire.
It has become so frequent that Frank Rich, a liberal columnist for The New York Times, said the laugh seemed to be the Clinton campaign's method of heeding complaints that she is "too calculating and controlled" and compared it to Democrat Al Gore's long kiss with his wife Tipper during the Democratic National Convention in 2000.
"Now Mrs. Clinton is erupting in a laugh with all the spontaneity of an alarm clock buzzer," Rich wrote.
Comic Jon Stewart on "The Daily Show" last week likened her to a robot with a robotic voice saying, "Humorous remark detected -- prepare for laughter display."
Presidential scholar Stephen Hess of George Washington University said Clinton's ability to laugh indicated she was becoming more comfortable as a candidate.