sap has one of dreams out to the side, his own hand pressing against dreams wrist to keep it down on the bed as sap traces his free hand gently over his tummy. he would pay attention to the spots that make him jump and squeal, and do the same with the spots that make him giggle and melt. he's using a fair amount of both, switching between wanting to make dream cackle and wanting him to make little chirpy giggles ):

surprisingly dream blurts it out while sap is being gentle - his pointer finger grazes a little too close to the middle of his tummy, right on the edge of the lil dip, and dream can't help himself. "s-sahahpnap! y-you sahaid you'd behehe nice thihis tihime! y-you're being mehehean!"

and from the look on saps face dream knows he fucked up. in fact he knew it the moment the words passed his lips, already being knowledgable on how cruel sapnap can actually be when he tries. but for whatever reason he says it anyway and now sapnap is just smirking down at him, his hand frozen on the warm skin of his tummy while the hand gripping his wrist slowly tightens, pressing it more into the bed

"this is mean?" sap would swipe his finger again closer to the side of his tummy and it makes dream squeak, slightly squirming to the side but not enough to truly get away. he'd squeeze his eyes shut as sap moved his hand off of his tummy, scared to see where it's going to touch down next. he doesn't feel anything though, and after a minute he hears sapnap mumble "I'll show you mean."

and that is just a tactic to get dream to open his eyes, which he does. they actually snap open, the fear in them causing sapnap to burst into giggles because "holy shit dude, your face!" which only makes dream blush harder than he had all night. it takes him a second to register but sapnap is hovering his hand over his vulnerable armpit, and it's only when he pulls at his wrist and finds it doesn't budge that dream truly realizes how much worse it could be

just as he starts to relax though, sapnap quickly kneads his pointer and middle fingers under his arm, wiggling them quickly with pressure to make dream scream. he nearly bucks sap off, which then prompts sapnap to make an offhand comment about how it feels like he's "back in texas riding the bulls!", but dream can't help it. he tries to turn his body onto the side to block his poor lil sensitive armpit but thankfully the fingers are gone as quickly as they appeared

"so we understand now that this isn't mean, right?" sapnap would go back to running his nails over dreams jumpy tummy which would send dream back into lil squeaky giggles again. he'd nod his head at sapnap and look up at him through his squinty eyes, giggling a little louder when sap starts giggling with him as well. sap would roll his eyes, bc of course he'd be giggling at dream, how could he not when he's that adorable? but he'd really wanna drive the point home, so he'd lean down close to dream's ear, letting his stubble tk the shell of it before he spoke