Panel 2 *DO...* (A sudden stop or pause) *Zupu...* (I think this is also a nonstandard sfx. Use your imagination. It "feels" like a slimy stab/penetration kind of sfx)
Panel 3 "......っ!" (That っ is important. Its a nonvocal letter, when used, you make a brief stop in your speaking before saying the next syllable. In this context, its like the brief moment after the realization that you got stabbed, and before you start screaming, that little niche of time where you realize that you got stabbed and start feeling the pain.)
Panel 4 "AAaAaAAAaAAaaAa" (VERY anguished scream. English is very horrible at portraying sfx like these.)
It could be more effective to switch the button into Post (without bumping) and Post with bumping.
That way we can separate the yukkuri who think Mister Vegetable just grow on its own and yukkuri who think Mister Human's Mister Vegetables are really easy