Provided/Providing (that) you clear your desk by this evening, you can have tomorrow off.

But move your head up and down and you will focus on objects at greatly varying distance - from very near to very far away.

He felt something falling on his head, and then he knew nothing about what happened later.

But it returned to the other dog, and put a paw on its head.

His infrequent visitors would ask things like "What are you going to do if a coconut falls on your head?" - given that the nearest doctor was hundreds of miles away.