Thumb Sucker #2

So riddle me this...All of a sudden Kate has become obsessed with sucking her thumb. I am puzzled because all of our kids stopped wanting their binkies at about 5 months. Reece decided his thumb was way better than plastic and Chase and Kate decided that they just didn't need to suck on a binky any more. We were ecstatic because that meant no more binkies to clean and keep track of and we wouldn't have to ween them later on down the road. So almost 5 months have gone by and Chase and Kate haven't needed anything to suck on for comfort. Last week, however, Kate found her thumb and has fallen in love with it. She sucks it while eating (thus spreading food all over everything), she sucks it while playing, she sucks it in the car, she sucks it in bed, she pretty much has it in her mouth at all times now. Huh. I just don't get it.