cook dinner / burn
I was cooking dinner when I burnt my hand.
prepare a sandwich / cut finger (you)
You were preparing a sandwich when you cut your finger.
do homework / hear a noise
I was doing my homework when I heard a noise.
drive / see a cat (she)
She was driving when she saw a cat.
buy an ice cream / meet a friend (he)
He was buying an ice cream when he met a friend.
walk / break
I was walking yesterday when I broke my leg.
drive / have en accident (they)
They were driving when they had an accident.