That's really interesting. I don't think spiders teach their offspring, so this must be an evolved trait.
I would guess the response surface is a function of wholesale cost, profit margin, and previous year's losses (or current theft).
So something that is frequently stolen and has a high wholesale cost and/or low margin will be locked up first. Toothbrushes are easy to conceal and likely have a low margin so lock them up.
Something else might sell for more, but has a higher margin or lower loss rate. You might lose one, but selling another 5 makes up for the loss.
It has to cost less to install an expensive cage and pay for the labor to open it up everytime a customer wants something from it than losing the item to theft.
Entrapment is enticing someone to do something they wouldn't do otherwise.
If you ask someone where to buy drugs, and they give you the name of their dealer, you're not entrapping the dealer since they normally sell drugs.
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