George cannot fight back against his grandmother physically or verbally, so he channels his feelings into the most creative act he can manage — mixing an extraordinary potion. Dahl turns frustration into invention.
The consequences of George's medicine are funny but also a reminder that mixing unknown things together is unpredictable. Dahl keeps the tone comic throughout.
Like many Dahl novels, this features a child oppressed by a cruel adult who is eventually overcome. Grandmother is given no redeeming qualities — she is purely an obstacle and an irritant.