Past perfect simple
Steph: Oh no. That looks painful. How did it happen?
Tony: Well, I was sitting at home when it happened. I had just finished dinner and picked up my glass of wine. The wine glass slipped out of my hand, spun and broke on the floor. I carefully got up and collected all the little pieces of glass. I thought I had collect all of them but one small piece was on the floor. I stepped backwards and my foot scraped along the piece of glass, leaving a big cut.
When did the accident happened: before or after dinner?
What caused the glass to break?
The wine glass slipped out of Tony's hand.
Had Tony collected all the pieces of glass?
No ("I thought I had = I hadn't).
Where was the last piece of glass?
What did the glass leave behind?
A big cut.