As you pay attention to each breath, see if there's any posture in your mind that is overreaching. You shouldn't be sitting like a cat waiting for a mouse to come out of its hole.
But maybe you should! It all depends on the stage of meditation you are in. In the earlier stage of concentration, sitting like a cat is exactly what is trained.
In fact the "cat and mouse" metaphor was used in a Dan Brown concentration meditation
It illustrated the focus of attention on thoughts at the moment they emerged.
Owl and mouse
The swirling sword