1) Ascertains 2) Catches a misdeed 3) Catches a whiff of 4) Catches the scent of 5) Discerns 6) Emulates holmes 7) Finds out 8) Finds the 100 tested 9) Makes out 10) Notices 11) Picks up 12) Picks up on 13) Picks up the scent of 14) Senses 15) Sniffs out 16) Spots 17) Uncovers 18) Uses radar 1) Espies 2) Makes out 3) Senses 4) Spots