Questions about prophecy.

[Rachel Ellington]

No: HPFGUIDX 140074

Finwitch says: 
Or that he wouldn't of killed this couple who had *thrice defied him* given half the chance? The few lines from the prophecy merely got him to prioritise the killing of the Potters... 


Rachel:
A few questions have come to mind about the prophecy- what exactly is meant by "thrice defied him?"  And WHY was Snape eavesdropping at the door?  Was Trelawney not thought of as a fake before she was hired by Dumbledore?  

Rachel.