For lack of better sources, I claim anecdotal evidence: My mother heard
"Kopf weg Schwanz weg: Has!"
when she was a child in the 1950s. It appears to be way older than this (I suppose I could check with some elder relatives, if necessary.).
The origin is undoubtedly the fact that all meat was a rare food and valuable source of protein in rural/poorer groups and times of famine or at least malnutrition were common in Europe for centuries. The superficial similarities between a roast cat and a roast rabbit1 together with a wider definition of meat fit for human consumption (beaver anyone?) brought cats on the table, too.
And of course there is the term "Dachhase" for cat - according to Wikipedia dating back to the siege of Vienna 1683 - also indicating culinary uses of domesticated cats.
In newer sources this is often refered to as a joke:
- There is a Swabian humorous story of the poor family who served the neighbour's cat at a wedding, complete with a boy spilling the beans afterwards with said quote. (Link here in Swabian dialect, see last paragraph.)
- The Movie "Der Etappenhase" (1937) has this substiution as main motiv.
1 note: both rabbit and hare was and is often called "Hase", the terms "Feldhase" = hare and "Stallhase" = domesticated rabbit are still used although not zoologigally correct.