The lever gets them out of the box, but after more and more trials, they stopped scratching at the bars and pushing at the ceiling.
杠杆让它们出了盒子，但在越来越多的尝试之后，它们不再抓栏杆和推天花板。
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When rats are trained to self-administer by pushing a lever, they'll push it over and over again — even hundreds of times — to get a single dose of cocaine.
Unlock the plunge mechanism by pushing up the plunge lock lever (R). Plunge the router down as far as it will go, allowing the bit to just touch the workpiece.