My friend at school showed me this Bible verse and was laughing and making fun of the Bible for it and saying it was ridiculous, what does it mean?

"A wife who intervenes in a fight to save her husband by grabbing his opponent’s testicles is punished by having her hand cut off (Deut 25:11–12)."

I need to be able to explain to her the meaning behind this.

My friend at school showed me this Bible verse and was laughing and making fun of the Bible for it and saying it was ridiculous, what does it mean?
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