### Clue: For Penn and Teller, according to Carroll, it's a driving mechanism (9)
### Answer: PROPELLER 
 ### Explanation: Definition: a driving mechanism
A charade of PRO ('for') plus PELLER, a , a construct 'according to Carroll' put in the mouth of Humpty Dumpty in *Through the Looking Glass*, blending 'Penn' and 'Teller'.