He drank the milk so he didn't drown. Then he threw the dead mouse outside. It shocked someone and someone accidentally tripped the bucket and the mouse got out???
Remember the only thing taken was the head.. If u understand it another way, the first thing taken was the head. Use this to eliminate the possibilities
Lets try another riddle hehehehe....
Oh,, a little warning... this riddle might be a little disturbing. Those who cannot take gross stuff please refrain from reading. kekkeke...