How do they know?

Firstly, I have already done a blip via my computer and talked about seagulls in port Isaac but it isn't showing!! This was my other point I'd like to make. Paracetamol- use them quite a bit especially for aches and pains probably a sign of getting older. What I can never work out is how they know where to find the sore bit and stop it hurting/aching? Because they do and I think that's amazing!