文本对齐:使用python提取匹配序列

我的目标是在两个文本段落中提取对齐的匹配序列.接下来是我的文字:

txt1='the heavy lorry crashed into the building at midnight'
txt2='what a heavy lorry it is that crashed into the building'

预期产量:

'heavy lorry'
'crashed into the building'

我的尝试:

def sequ(s1,s2):
    _split1=s1.split()
    _split2=s2.split()
    _match=''.join(list(set(_split1) & set(_split2)))
    return _match

print sequ(txt1, txt2)

Result: heavybuildingintocrashedthelorry

......扭曲的结果.

有关如何达到预期结果的任何建议？谢谢.