''On matters of physics, I always regarded Stephen [Hawking] as an oracle and just a few words from him could yield insights which would have taken weeks of work on my own. I was therefore particularly lucky to share an office with him since this gave me privileged access to there insights. However, Stephen is only human and not all encounters led to illumination. Once, while sharing an office with him at Caltech, I asked him a question about something which was puzzling me. He thought about it silently for several minutes and I was quite impressed with myself for asking something which Stephen couldn't answer immediately. His eyes then closed and I was even more impressed with myself because Stephen was clearly having to think about it very deeply. Only after ten minutes did it become clear that he had fallen asleep!''
Carr, ''Primordial Black Holes'', in Gibbons et al. (eds), The Future of Theoretical Physics and Cosmology: Celebrating Stephen Hawking's 60th Birthday, p. 258.