“叫什么来着”问话人曾经知道，现在一时想不起来，希望得到提醒。

What is this called?The speaker knew it before but now he has just forgotten about it and would like to be reminded.

因此，我难以想象当我的母亲告诉他我即将出生的时候，他竟然兴奋地一时想不起来把车钥匙放在哪里了。

It is difficult, therefore, for me to imagine that he became so excited when my mother told him I was about to be born that he momentarily misplaced his keys.