The mouse freezes when it lands in his hand, just. Waiting.

Watching him proceed.

It stays still even as Walter walks and speaks, and only when he stops at the bushes turns around and squeaks at him, once.

And then it jumps off his hand, and at that moment Walter is hit with an echo. The resounding heartbeat this time will, deep down, remind him of listening to his mother's heartbeat in the womb, and make a feeling of safety and warmth flow through him.

And whatever he echoes, it will be something good that made his preincarnation happy.