ELI5 Hostile Takeovers - explain Twitter's poison pill like I'm 5?

In business, what is a hostile takeover? How does it work? How can a board of directors prevent a hostile takeover? What is a poison pill? Can a board choose not to use a poison pill once it has been set up? What do Microsoft, Netflix and Papa Johns have in common?

... we explain like I'm five

Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: vonshavingcream, georgeoscarb, oohcharlie and phage0070

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