Изменение глагола

Show the white feather - струсить, смалодушничать

Heely Clinker, who was in his regiment, said that he not only cheated at cards but showed the white feather (W. Thackeray).

Oh, my dear fellow, don't worry. I've been frightened too often myself to blame anyone who shows the white feather (W.S. Maugham).

Never before in the history of the service had a ranger shown the white feather (0. Henry).

There were caricatures of all three generals "showing the white feathers"... (R. Aldington).

Изменение сложного глагола является показателем цельнооформленности, так как оформляет все сложное слово в целом (ср. mass-produce - mass-produces - mass-produced - mass-producing и т.п.).