When Alexander Fleming came back from holiday he noticed that mould contamination on an experimental plate had killed a pathogen. Fleming wondered 'Why?' Careful observation, rigorous scientific thinking and painstaking experimental work led to the discovery of pencillin.

When a glass flask was knocked to the floor in Eduard Benedictus' laboratory he was surprised to discover that the glass had shattered but somehow the flask stayed together. It was all the result of his assistant failing to clean away the remains of the previous experiment. Reading about a rash...