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It's not the pens that keep in the sheep. Staying in the pens is what they're trained to do.

They don't need to be thinking of what happens when they aren't going to be kept in the pens anymore, so they're trained not to think about that.

sheeppens.jpg
IMG source - @lighteye

Were the sheep aware of the slaughterhouse, they wouldn't stay in the pen. Infodemics are bad husbandry.

How accurate you are