Graorin shushes Athedru. "Get Dreev out of the way," he whispers calmly. For the first time in three days he feels comfortable - he's in his element again, in the forest, facing beast rather than man, and, most importantly, he has the right spell.

Knowledge (nature) check to see if, despite its size, anything about this crab might make casting Calm Animals anything but routine:
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(1d20+4)[16]