A video from Wroctaw Zoo has gone viral, racking up millions of views across social media. The unlikely "challenger" is a male Chinese muntjac - a small deer species from Asia - boldly trying to prove who's in charge, even when his opponent weighs 1.7 tons. Zoo staff say the explanation is simple: the female is in heat, testosterone is surging and instincts take over. Sometimes, even the smallest body hides a fearless warrior.

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