The L.B. has to live from read words. It steals single lines from the prose or poetry you just read. The really advanced ones will extract them after you read them, making it impossible to think of one specific line. The young ones sit on the page that is read and eat the line right from under the eye. Maybe it is just a game and they survive on something else. I am not sure.
How to fight it
Annoying but depending on what you read, totally insignificant. The L.B. just has a chance, if you are not properly concentrating on what you just read. gab