The correct answer is "Wrap the thumb in gauze, place in a bag and then on ice".
Wrapping the cut-off finger in gauze or in any cloth, should be immediately placed in a bag then put on ice for it to be chilled. the thumb should not be exposed directly to the ice, or it will cause ice burns, wherein it will cause the thumb to not get sewn back. the ice is used to chill the thumb, to prevent the it from decomposing, not for freezing it.
