So the poison pill seems to be a massive increase of the issued stock issued from the company directly,, at 1/2 price of the street value, thus diluting the value of the takeover groups stake.
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The Rights Plan is similar to other plans adopted by publicly held companies in comparable circumstances. Under the Rights Plan, the rights will become exercisable if an entity, person or group acquires beneficial ownership of 15% or more of Twitter's outstanding common stock in a transaction not approved by the Board. In the event that the rights become exercisable due to the triggering ownership threshold being crossed, each right will entitle its holder (other than the person, entity or group triggering the Rights Plan, whose rights will become void and will not be exercisable) to purchase, at the then-current exercise price, additional shares of common stock having a then-current market value of twice the exercise price of the right.
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