The PhD Dissertation Explained:

“‘What is it, then?’
‘Nothing.’
‘What do you mean, nothing?’
‘Nothing of importance.’ [...] ‘I’d rather not talk about it.’
‘Come on, professor, out with it.’
‘It’s, er, a doctoral thesis.’
Smyke laughed. ‘That’s a relief. I thought it was some frightful disease.’
‘So is a doctoral thesis, in a way.’”

Walter Moers, Rumo & His Miraculous Adventures, (p 142).