Random skeleton appearing in my home?

Well I was on minecraft and then at night on easy mode I decided to go to sleep. I had all doors closed at night except the extra one in front of my bed. But the front doors were closed so nothing could get in. Then I was disrupted at night by a skeleton even though there are no holes in my house , all doors are closed except the one to my bedroom . I have 4 pet wolves in case that could of caused it. My bed is not touch any walls in my house , my door is a single door and the walls around my bedroom is made out of wood. I have plenty of torches inside. Why did this happen?