Be careful when handling a razor edge.

Be careful when walking through the minefield.

Be careful of the undertow when swimming in the ocean.

She is such a fusspot when it comes to cleanliness.

He is a fumbler when it comes to technology.

There was a murmur when she entered the room.

When do you leave here?

When shall I come for you?

The histogram shows when a crossing occurs.

There was an awkward silence when he appeared.