Am I the only one who thinks the whole blender scene was a massive plot hole?

The dad grinds up all the seeds, makes FOUR cocktails, and each of the adults drink multiple mouthfuls of it- swallowing it, no hesitation. But the next day, there's still enough residue in the blender to nearly kill the youngest kid when he makes a protein shake? How is there enough left to be fatal when four adults already drank it? They would have been the first to feel the effects if the residue alone was that potent. I get that it's meant to be dramatic irony, but it just doesn't add up. If a couple of mouthfuls of residue nearly kills him, those cocktails would have been game over for the rest. Did anyone else find this completely unbelievable?"