Let's analyze the options:
- Nest, Stable, and Hole are all places or structures related to specific animals.
- Nest is a place where birds live.
- Stable is a place where horses are kept.
- Hole refers to a structure often associated with animals like rabbits or moles.
- Boat, on the other hand, is a man-made object used for transportation on water, not related to any animal-specific habitat.
Thus, Boat is the odd one out.
Therefore, the correct answer is \( \boxed{4} \).