同类相吸

Like attracts like.

like / same / similar / together / alike / with

see 衚衕|胡同[hu2 tong4]

similar / same type / alike

kind / type / class / category / similar / like / to resemble

each other / one another / mutually / fret on the neck of a pipa 琵琶[pi2 pa5] (a fret on the soundboard is called a 品[pin3])

appearance / portrait / picture / government minister / (physics) phase / (literary) to appraise (esp. by scrutinizing physical features) / to read sb's fortune (by physiognomy, palmistry etc)

mutual attraction (e.g. electrostatic) / to attract one another

to breathe / to suck in / to absorb / to inhale