Ní ọjọ́ 9 oṣù Ọ̀wẹwẹ̀, 1947 Grace rí àṣìṣe kan ní orí ẹ̀rọ Mark II tí àfòpiná kan tí ó kú sínú rẹ̀ fà. Ó yọ kòkòrò náà ó sì lẹ̀ ẹ́ mọ́ ìwé àkọsílẹ̀, báyìí ni a ṣe hu èdè ìperí kòkòrò aṣàṣìṣe orí ẹ̀rọ ayárabíàṣá. Láti ìgbà náà lọ ni “kòkòrò aṣàṣìṣe” di èdè ìperí fún ìṣàpèjúwe àṣìṣe tàbí àléébù orí iṣẹ́ àìrídìmú kan.
On the 9th September, 1947 Grace traced an error on the Mark II to a dead moth that was trapped in a relay. The insect was carefully removed and taped to the log book and the term computer bug was coined. Henceforth the term “Bug” was used to describe any errors or glitches in a program.