Please don't waste your time, Phillipp and Bob C., both your contributions are far too valuable!
Now here's what I think:
1. The words for tail and "prick" or what you choose to call it are different in Spanish, aren't they, cat...? In this context, tails, and nothing else.
2. @catatonia, it might help if you told us what book this is from (somebody might have the Spanish version at hand) and if this is for a serious literary translation or for some other purpose. Slightly OT, but necessary: What is this unreliable German source? For anybody who might think "der Traum geborene Vorschlag" is proper German: IT IS NOT. Even after the unfortunate spelling reform, it's crap and just a sign of what this reform did to innocent minds. Therefore, for the record, it is and remains der traumgeborene Vorschlag. Anything else is not only wrong spelling, it's an assault on grammar.
3. @Bob's 24: Die Liebe wäre sicherer, aufrichtiger und seliger, wenn die Hände frei wären, um allein ihre Liebespflichten zu erfüllen, während an unserem Rücken die Gewissheit eines gegenseitigen Verständnisses, einer innigen Liebe umschlungener Schwänze bestände. "Love would be more assured...", I'd say. Bob translates the clause: if, on our backs, we had the assurance of mutual understanding and tender love of intertwined tails, and catatonia: if while on our backs there existed the certainty of a mutual understanding, of a profound love of intertwined tails. "While on our backs" is certainly wrong (I agree with Bob), but "there existed the certainty" is surely a better rendering of the German. And I'd opt for "down our backs".
4. The opening phrase translates better as "if we, men or women, still had our tails". The "still" is contained in the "unsere" in German. "If we had tails" provokes the answer "but we don't have tails". "If we had our tails" means if we had them, because they belong to us. "If we still had our tails" means if we had them back (because we had them, once). This is exactly what the German implies.
Hope there aren't too many typos and this is helpful.