Just "2 * 2" is near enough instant ("About 25,270,000,000 results (0.64 seconds)") but "2 * -2" takes its time ("About 0 results (5.16 seconds)").

Some sort of conflict between the "ignore keyword using hyphen prefix" and the "is it a calculation" detection, causing the search itself to time out and produce zero results? Searching with quotes ("2 * -2") is fast ("About 25,270,000,000 results (0.49 seconds)") but no calculator is shown.