tease/at

What would be the difference in meaning between "to tease at" and "to tease" here?

Quote:

His thumb came up to tease at the corner of her mouth, softening her expression
even as the bitterness ached within her.

Quote:

To her shock, his tongue came out to tease at the palm of her hand, and,
inexplicably, Catherine arched off the bed again.

Quote:

I jumped at every noise; darkness seemed to tease at the corners of my eyes.

<His thumb came up to tease at the corner of her mouth, softening her expression even as the bitterness ached within her.>
His thumb touched the corner of her mouth gently and fleetingly.


<his tongue came out to tease at the palm of her hand>
Pretty much the same as above. The tip of his tongue barely touched her palm.

<darkness seemed to tease at the corners of my eyes>
Not so sure here. Possibly that darkness was barely noticeable or the room was just becoming dark.

I asked this, RayH:

<What would be the difference in meaning between "to tease at" and "to tease" here? >

e.g

His thumb came up to tease at the corner of her mouth, softening her expression even as the bitterness ached within her.

His thumb came up to tease the corner of her mouth, softening her expression even as the bitterness ached within her.