练开膛

[RogerGe]

What does 练开膛 mean? Here is the context, from 黄金时代：

我过二十一岁生日那天，打算在晚上引诱陈清扬，因为陈清扬是我的朋友，而且胸部很丰满，腰很细，屁股浑圆。除此之外，她的脖子端正修长，脸也很漂亮。我想和她性交，而且认为她不应该不同意。假如她想借我的身体练开膛，我准让她开。所以我借她身体一用也没什么不可以。唯一的问题是她是个女人，女人家总有点小器。为此我要启发她，所以我开始阐明什么叫做"义气"。

 

Pleco says "cut open the chest (of a pig, chicken, etc.); draw" which doesn't make much sense.

[陳德聰]

Have you read up til there already? 陈清扬 is a doctor. He's saying he'd let her practice cutting him open so she shouldn't have a problem letting him mount her.