Actually itโs any time you enter a variable at the command prompt. Thatโs even funnier because I guess giving Prolog nothing but a variable name as a query is the same as asking it to tell you the meaning of the universe.
8 ?- JABBERWOCKY.
% ... 1,000,000 ............ 10,000,000 years later
%
% >> 42 << (last release gives the question)