2511. Read that back to me! What do these characters have in common? 売 請 討 威 泡

They all have a reading that is the same backwards.  

売  BAI, u(ru) - sell

請  SEI, SHIN, ko(u), u(keru) - ask for, receive

討  TOU, u(tsu) - attack

威  I - authority, dignity, majesty, threat

泡  HOU, awa - bubble, foam