Full Idea
Two animals with all motor nerves cut will have the same actual and potential behaviour (i.e. none), but if only one has uncut pain fibres, it will feel pain where the other won't.
Gist of Idea
Total paralysis would mean that there were mental states but no behaviour at all
Source
Hilary Putnam (The Nature of Mental States [1968], p.57)
Book Reference
'The Philosophy of Mind', ed/tr. Beakley,B /Ludlow P [MIT 1992], p.57
A Reaction
This is a splendidly literal and practical argument against behaviourism - if you prevent all the behaviour, you don't thereby prevent the experience. Clearly we have to say something about what is inside the 'black box' of the mind.