In Lost Others are known to take children, but as later revealed, Alex was only taken because Ben was sent to kill Rousseau and couldn't kill a child.
Later the kidnap Walt who claimed Others did some experiments on him, and they later say that "we received more from Walt than we expected".
What is it they're talking about?
Even though this is an old question, I've recently discovered this episode called Room 23 in which we seem The Others running at the sound of the alarm and Juliet telling Ben that He did it again and took him outside to see a bunch of dead birds.
Later on Walt tells Michael that they made him take tests to which we did not get a definitive answer but most probably in electricity and magnetism since birds sense and use magnetic fields in their migrations.
