Possible Clues:

• "Psst!"
• 'Psst!'
• ''Psst!''
• Attention-getting call
• Attention-getting shout
• Kin of 'pssst!'
• 'Pssst!' kin
• "Oh, hi!"
• 'Pssst! Over here!'
• 'Oi, you need to explain toughie', he said. By the way, it's impossible! (3,3,5,3,3,4)