The intrusion
The intrusion has to be environmental and pervasive, affecting everything. For example, it can't be a cat, but it could be a plague of cats. Ideas could include:
- Heat
- Wind
- Snow
- Cold
- Mist
- Damp
- Silence
- Noise
- Sunshine
- Pollen
- Fire
- Water
- Insects
- Animals
The intrusion could also be something psychological that's affecting the whole environment:
- Nerves
- Contentment
- Anxiety
- Resentment
- Joy
- Anger