expression, godan verb (-ru)
do something impossible; attempt the absurd
Idiomatic expression literally meaning 'to cut one's belly with a pestle', used to describe attempting something utterly impossible or absurd.
そんな計画は連木で腹を切るようなものだ。
That plan is like trying to cut your belly with a pestle—completely impossible.
The expression is a fixed idiom; the literal image of using a blunt wooden pestle (連木) to perform seppuku (腹を切る) conveys impossibility.