you'll be able to feel the babies head through the membranes if the head is well down on the cervix, it just makes a slippery feel over the head, if the membranes are gone it feels more 'rough' ( not sure if thats the right word). If it feels mucousy to you that sounds like the membranes slippery over the head so don't stress. Sometimes the membranes are 'bulging' once contractions start and that feels like a balloon coming through the cervix, you wouldn't feel the babies head then but you might pop the bag so be careful in that situation.