The classic one is Ax in dummy, Txxx in your hand. Win the ace, if RHO has Hx you block the suit. This also applies for Ax opp 9xxx as if RHO has HH doubleton, the suit blocks. HH doubleton is likely if the suit is 5-2 since LHO would lead an honor with QJTxx or KQJxx, and might with KQTxx or KJTxx.