Q. Read carefully a brief summary of one of the investigations of Sherlock Holmes : "While investigating the murders of Stangerson and Enoch Drebber he got into conversation with fellow detectives which runs as follows : "The last link My case is complete.... Could you lay your hands upon those pills". After he got those pills, Holmes cut one of them, dissolved it in water and placed it in front of the terrier. Contrary to his expectations, the animal survived. Though disappointed a bit, he thought fora while and then cut the other pill, dissolved it, added milk and placed before the animal. The moment it licked, the animal died. Those were the pills present at the scenes of crime. Which one of the following aptly describes the method which this passage indicates ? 

1. Imagination
2. Experiment
3. Observation
4. Thought experiment