In reference to this post, several e-mails along these lines:

Subject: Isn’t it “another think”?
Rather than “another thing”? Basically to contrast with the first conditional clause, i.e., “if the xxx think yyy, they’ve got another think comin’!”

Answer, provided by another e-mailer:

Subject: You’ve Got Another Thing Comin’
Who knew Harry Reid was fan of Judas Priest?

It turns out that this is an example of an eggcorn. I had no idea.