He feels muscle contractions every day.

He suddenly fell down as his leg underwent a spasm.

This sweater may shrink if you wash it.

This sweater shrinks when washed.

My uncle gave me a birthday present.

Everyone was paying their respects in silence.

I mailed a letter at the post office.

We held a party to celebrate his promotion.

We celebrated his success.

There are a lot of Medicago polymorpha growing in this field.