U.S. President Donald Trump took his oath of office on Monday with his right hand raised, but without placing his left hand on the two Bibles that his wife Melania held as she stood by his side.

The apparent oversight has no practical impact, academics say, but it roused curiosity online. 

Despite the inauguration pomp and a bracing speech, the top thing Americans searched for on Google in relation to Trump on Monday afternoon was about him not placing his hand on the Bible.

Rev Franklin Graham, who delivered prayers at the ceremony, told Premier Christian News that Trump did not place his hand on the Bible due to time constraints.

Swearing on the Bible is not an essential part of taking office. Article II of the US Constitution simply states that the chief executive of the United States must recite the oath. 

John Quincy Adams was sworn in on a book of US law, representing his commitment to upholding the Constitution.

Theodore Roosevelt also chose not to swear on a Bible, when he was hastoily inaugurated after William McKinley’s death. After John F Kennedy's death,  Lyndon B. Johnson’s placed his hand on a Catholic prayer book belonging to his deceased predecessor. 

Despite the lack of contact with the Holy Book, Trump did close his speech with "So help me,God."

“There’s nothing in the Constitution that says the president has to connect this to God in any way,” Jeremi Suri, a University of Texas, Austin history professor and presidential scholar, told Reuters.

“The oath is to the Constitution."

Trump had chosen the Bible the 16th President Abraham Lincoln was sworn in on and one given to Trump by his mother, his transition team said.