Past simple vs continuous
One thing is going on and then something else happens:
*you are having dinner from 17:00 - 18:00 and at 17:25 you get a phonecall
I was having dinner when I got a phonecall.
*You are taking a shower from 8 till 8:15 and at 8:07 the doorbell rings.
While I was taking a shower the doorbell rang.
Indicators: while / when (terwijl, toen)