Theory of mind and experimental representations of fictional consciousness

Let me begin with a seemingly nonsensical question.1 When Peter Walsh unexpectedly comes to see Clarissa Dalloway "at eleven o'clock on the morning of the day she [is] giving a party" and, "positively trembling," asks her how she is, "taking both her hands," "kissing both her hands," thinking that "she's grown older," and deciding that he "shan't tell her anything about it... for she's grown older" (40), how do we know that his "trembling" is to be accounted for by his excitement at seeing his Clarissa again after all these years, and not, for instance, by his progressing Parkinson's disease?.