Asriel taps his brother on the shoulder, explaining what was happening. However, Frisk didn't really care, continuing to put food into his mouth, and by extension, into Asriel's belly.
Feeling like he deserved more than to be a fat container for Frisk's nearly endless binges, he tried to take the food away, small amounts of pudge adding onto him by the minute, the sounds of digestion growing slightly louder with more food put into his already full stomach.
Frisk reacted as you'd expect a hungry person to react to having their food being taken away. He struggled with Asriel, the goat brothers dropping to the ground, rolling around, with Frisk eventually pinning his chubby brother down on the ground, and wouldn't you know it, right next to the fridge.
Opening it up, he looked inside, for the most fattening food inside. Ruling out most of the contents, Frisk was left with two options, either half a pie or half a cheesecake.
Unable to pick one, they take both out, balancing them on a single hand using a plate. Grabbing a piece of cheesecake, he's about to put it to his lips when an idea occurs to him.
Instead of eating it himself, he jams it into Asriel's mouth, forcing him to swallow it, and then he grabs a chunk of the pie, cramming it into Asriel as well.
Pausing to see how Asriel reacts, or rather, how his paunch reacts, Frisk notices it beginning to swell a bit, then stop. He considers his options, thinking about what to do next.