A bug…..
Read some interesting trivia in a book, “The Silicon Boys†by David A. Kaplan on origin of “bug†i.e. a computer bug….
The University of Pennsylvania’s ENIAC (Electronic Numerical Integrator and Computer) in 1946 was the first attempt at a large scale digital computer. It was a huge thing and had 18000 vacuum tubes. The warmth & light of ENIAC’s tubes presented a problem – moths liked them and would trigger short circuits. Hence “computer bug†meant a problem inside and “debugging†meant fixing it!