Please solve the case below

Last Sunday, Greg's friends dropped by to watch the Superbowl game on T.V. Greg had purchased cans of cola from his local corner store, which he offered to his guests. The cans were not past the stale-date. One friend, Bob, took one, and noticed a strange taste as he took his first sip. He poured some of the cola into a glass, and as it was a strange colour, didn't drink the rest. Bob subsequently became very ill, requiring hospitalization. Analyse this case as outlined in the course