UrsusArctos: After the bafflement that he felt fifteen episodes ago he has an appropriate explanation. Of course, he's not the first person to think they're being replaced by Rei, but this idea doesn't take hold in his mind in quite the same way as it already is with Ritsuko. It does make me wonder if Ritsuko would have acted differently in Episode 23 if she knew this particular thought had crossed Shinji's mind.