(mechanics) fluid mechanics

specialist; expert

a fluid (any state of matter which can flow)

he / distal demonstrative, something far off removed from both speaker and listener: that / boyfriend

distal demonstrative, something far off removed from both speaker and listener: that, yon / particularly, male personal third person pronoun: he / by extension from he: boyfriend

he; boyfriend

speciality/specialty; subject of study; subject of expertise; area of interest; profession

a house / one's own home / a home, household / a family

mechanics (a branch of physics)

outside of one's field of expertise