I shudder to think of it.

Come to think of it , he is wrong.

The secret of success is not to think of failure.

What do you think of this sweater?

I can't think of the answer offhand.

Now that I think of it , it's too small - that ring.

Come to think of it, I forgot to buy milk.

I can't think of the answer off hand.

What do you think of our new abode?

If you like, you can think of it as a sort of magic.