He'd been thinking that, every so often, ever since the idea had popped into his head.

That was the conclusion he'd reached when the idea popped into his head earlier.

You see, these ideas on how to do things just pop up and away I go.

He was startled by the way that idea popped into his head.

One day, an idea popped into his head, as ideas constantly do.

Then an idea popped into my head, but that couldn't be it.

It seemed obvious, once the idea popped into his head.

A slightly odd idea popped into my head one evening.

She paused then, because an idea had just popped into her head.

I get it from life, and ideas pop into my head.