Possible Clues:

• Looking astonished as assistant's back in time
• With mouth wide open a cavity's visible finally
• Wide-open, as a mouth
• Clearly surprised it's used for cooking next to gym
• Staring open-mouthed
• Awestruck, perhaps
• Love of one's fellow man, to Greeks
• Awestruck, head academic turned page.
• Displaying surprise, in a way
• With mouth hanging open in shock