Ok, my humour got the better of me yesterday with the "ouch" comment. I did get the probable intent - a set of quick, light bounce off the keys as if there were thumb tacks. That is sort of how one would play to get that kind of sound ..... sort of. I don't like the imagery because personally, if I'm told to imagine something, I imagine all of it. I'd imagine the pain or fear of pain that comes with bouncing sensitive fingertips off of thumb tacks. My hands would hold back and tense up and recoil, part of my going toward pushing the keys, part of me pulling back - there is an emotion or feeling associated with poking thumb tacks. That is probably also why I wrote "ouch".
Find out what kind of touch / movement you need, experiment with that. Use your ears and listen to your body as you experiment. The "thumb tack" idea is a starter to bring you there, clumsy as the imagery might have been expressed.