两者都是企业可以采取的反收购措施。

Pac-Man defense指反噬防御，亦称帕克曼防御。

反噬防御就是指在反收购中，目标公司以收购袭击者的方式来回应其对自己的收购企图。公司在遭到收购袭击的时候，不是被动地防守，而是以攻为守、以进为退，它或者反过来对收购者提出还盘而收购收购方公司或者以出让本公司的部分利益、包括出让部分股权为条件，策动与公司关系密切的友邦公司出面收购收购方股份，以达围魏救赵的效果。

反噬防御是根据美国一个流行的电视剧命名的，剧中的人物在吃自己之前都会尽力吃了其他人。在反收购中，是指目标公司以收购袭击者的方式来回应其对自己的收购企图。由于它的极端性，这种方式通常被认为是“世界末日方式”。

The Pac-Man defense is a defensive tactic used by a targeted firm in a hostile takeover situation. In a Pac-Man defense, the target firm then tries to acquire the company that has made a hostile takeover attempt. In an attempt to scare off the would-be acquirers, the takeover target may use any method to acquire the other company, including dipping into its war chest for cash to buy a majority stake in the other company.

crown jewel defense指皇冠之珠。

皇冠之珠指的是目标公司将其最有价值、对收购人最有吸引力的资产出售给第三方，使得收购人对目标公司失去兴趣，放弃收购。

In business, when a company is threatened with takeover, the crown jewel defense is a strategy in which the target company sells off its most attractive assets to a friendly third party or spins off the valuable assets in a separate entity. Consequently, the unfriendly bidder is less attracted to the company assets. Other effects include dilution of holdings of the acquirer, making the takeover uneconomical to third parties, and adverse influence of current share prices.

以下为相关双语示例，供参考：

For some companies, the Pac-Man defense is one of the few options available when faced with a hostile takeover attempt. Without getting aggressive and fighting back, the company may have no chance of surviving. However, on the downside, the Pac-Man defense can be an expensive strategy that may increase debts for the target company. Shareholders may suffer losses or lower dividends in future years.

对于一些公司来说，面临恶意收购时，反噬防御是为数不多的选择之一。如果不积极反击，公司可能就没有生存的计划。但是，缺点是，反噬防御是一种代价昂贵的策略，可能会增加目标公司的债务。股东可能会在未来几年遭受损失或减少股息。