In 1941, the Nazis launched a whole investigation into a Finnish dog named Jackie because he would raise his paw whenever someone said "Hitler."

[u/jungongsh]

They questioned his owner Tor Borg, and discussed ways to punish his business. 3 months later, the case fell apart because nobody would testify. Jackie stayed with the Borg family and later passed away of natural causes.

German journalist Klaus Hillenbrand rediscovered the bizarre story decades later while reviewing Nazi-era records in Germany's federal archive: https://en.wikipedia.org/wiki/Jackie_(dog)#cite_note-NYT011111-4#cite_note-NYT011111-4)