on the plains of the Serengeti, a dung（粪） beetle（甲虫） rolls his perfectly sculpted ball of dung（粪） away from competitors. In this Canadian river, a beaver rushes（冲） to reinforce（增援） her dam（水坝） as it threatens to burst. As the snowball thunders down the mountainside（山腹）, gaining（获得） momentum（动力）, the Arctic foxes run for cover. I can't stand these nature programs. Always the same story and not a rational（合理的） actor in sight. What else is on?

  It's April 1954 and Vietnamese nationalists are on the verge（边缘） of victory（ [C] 胜利） against French forces fighting for control of Vietnam. Their victory could lead to an independent Vietnam under Communist（共产主义的） leader Ho Chi Minh. The United States President Dwight D. Eisenhower is holding（拿住） a press conference to comment on these developments. Well, if you really must. Eisenhower claims that by virtue（善） of what he calls the falling domino principle（原理）, Communist control of Vietnam would be the beginning of a disintegration that would be certain to cause incalculable loss.

  The beetles and the beavers may be beyond（在…的那边） my reach（范围）, but surely here's someone I can reason with. Now, Mr.President, let's take a deep breath, shall we? It's a big leap（跳跃） or, one might say, a long slide（滑） from communist（共产主义的） governance（统治） of Vietnam to the global spread of authoritarian communist（共产主义的） regimes. It's as if we were to say you were clothed（给…穿衣服）, now you're in your underwear, so soon everyone in the world will be completely naked（裸体的）. Don't worry, I may have that power, but I promise not to use it. Now, as I was saying, this kind of argument where one step, let's call it A, kicks off a string of events that inevitably（ 不可避免地） culminates（到绝顶） in an extreme scenario（方案）, let's call it Z, is known as a slippery（滑的） slope（斜坡）.

  Many such arguments focus on catastrophe, but the slope to an extreme positive outcome（结果） can be just as slippery（滑的）. The trouble with this kind of argument is that in presenting Z as the inevitable（必然的） outcome（结果） of A, it almost always overstates the likelihood（可能性） that Z will happen if A happens.