An explorer was taken prisoner by a cannibal tribe.

The tribe leader goes up to the explorer and
puts a hourglass in his left hand while he says that is a 4 mn
then he puts a 7mn hourglass in the explorer's right hand.

Then he explains to the explorer that if he succeeds in measuring exactly 9 mn he will be liberated,
else if shouldn't be the case he would be honoured with his presence as main dish for the dinner.

Then he look at him right in his eyes with a smile flickering around his mouth and he says : "Start now".

What did you do in his place?