Luka Lucic shows off his rare skill.

Luka Lukic, 6, is an attractive boy. (Marko Drobnjakovic/A)

But other experts remain skeptical.

"I doubt very much that someone is magnetic," said Patrick Regan, a physics professor in England. "Humans are made of the wrong material to be magnetic."

"It would be pretty unsafe to have metal objects sticking to you against the force of gravity," he said. "You couldn't switch something like that off - unless it's fake."

Luka's father, Slavisa Lukic, said doctors have told them the boys are otherwise healthy.

"Nobody can tell us why this is happening," he said.

David's mom said the magnetic attraction appears to wane when the boys sleep but switches back on when they are awake and moving around.

The family says they were alarmed at first but have gotten used to the unusual phenomenon and all the attention surrounding it.

"It was a shock at first, but now we just try to keep the knives away from them," Petrovic says.