När det gäller frågor 1 och 3: John såg (genom fönstret) båda männen skulle ta sina piller. Han antog att Sherlock skulle svälja pillret, så han bestämde sig för att skjuta.
När det gäller fråga 2: Det vet vi inte, men om Sherlock hade rätt i sitt avdrag var det bara ett giftigt piller. Från Baker Street wiki :
Summing up his observations, Sherlock ventures that the "game", as the cabbie calls it, is about his children. The cabbie confirms he has been estranged from his children for three years and has been told that he is dying. He adds that the inheritance he will leave for them is only meagre, And in that moment, focusing on his children and his mortality, the cabbie looks to the pill bottle on his left. Sherlock deduces that is where death is.