Oops.

At the end of a painful, meandering response concerning federal government departments he would abolish, Perry said there were three — but named only two. “I would do away with Education, the – Commerce and, let’s see, I can’t. The third one I can’t."

Then Perry offered an apologetic "Oops," as if he had flunked a test. Watch the video.

Almost immediately after the slip, Perry's Intrade stock dropped from a 8.6 percent chance to 4 percent to become the Republican nominee in 2012, according to Nate Silver of the Times FiveThirtyEight blog. The stock currently stands at 4.9 percent.