Here's the deal: Back in 1996, during the so-called "partial birth abortion" debate, Feingold and some other Senators supported a ban on the exceptionally rare procedure, but wanted an exception when the health of the mother was at risk.
Senator Rick Santorum was the floor manager trying to get the partial birth abortion ban passed and as Senators spoke in favor of a health exception, Santorum asked them what they do in the hypothetical (and impossible) situation where a women was having the procedure and the fetus somehow fell out of the birth canal and was outside the woman and alive.
Russ Feingold was in a committee hearing and late to the debate and was unaware that Santorum was asking this question. As Santorum started to ask his question of Feingold, Senator Barbara Boxer pulled him aside and attempted to warn him of Santorum's question.
Boxer's interuption is not shown on the video, but Santorum makes mention that Boxer is talking to Feingold as he is asking his question.
If you've ever had two people try and talk to you at once, you know that you usually end up not hearing either person. That's what happened here. Feingold never heard the question.
What is not shown on the video, is that when Feingold realized what the question was, he immediately corrected the congressional record to reflect his actual view.