Challenge!!

The BUGS want to challenge all the parents (grandparents, dear friends, neighbor Bob...):

How many sounds does the regular past tense ending "-ed" make?  

Can you predict when it will make each sound?

Reply in the comment section with your answers!
 (Guesses are totally accepted but might make us chuckle.  We know grown-ups weren't taught all the awesome grammar rules like we learn now!)

(You can email-a-teacher for a hint!)