First of all I ask 2-3 students to read the text. then let them try to guess. as soon as the answer is found i work with them a second activity with the same riddle. I some of them to retell the answer in Past Simple. next student does the same but in Present Progressive,or Futurei or using MUST. It's up to you. Very often they grumble, but work it.
the key is:
he takes a goat goes back takes cabbage leaves it and takes goat back then takes wolf goes back takes the goat