“split your sides”意思是“捧腹大笑；笑破肚皮”。

【例句】
Did you see the stand-up comedy show on TV last night? It was so funny, I almost split my sides.
你昨晚看电视上播的单人喜剧了吗？太搞笑了，我快笑死了。

We practically split our sides laughing/with laughter watching Peter trying to get the toy into the coat.
我们看到peter试图把玩具放进衣服里，几乎笑得直不起腰来。