### Clue: Stares open-mouthed at girl taking on monkeys (5)
### Answer: GAPES 
 ### Explanation: Definition: Stares open-mouthed
 G(abbrev. for "girl", as in "gf"/girlfriend?) **plus**(taking on) APES(primates/"monkeys" in general use, though apes are larger-sized than monkeys).
… not just any girl.