Very funny joke about Germans and kinky sex

A German guy approaches a prostitute and says "I vish to buy sex vit you" "OK" says the girl, "I'll charge 100 Euros an hour" "Ist goot, But I must varn you, I am a little kinky" "No problem" she replies cautiously, "I can do a little kinky" So off they go to the girl's flat, where the German produces four large bedsprings and a duck caller. "I vant you to tie ze springs to each of your limbs.." The girl finds this very strange, but complies, fastening the springs to her hands and knees. "Now you vill get on your hans and knees." She duly does this, balancing on the springs. "You vill please blow zis vistle as I make love to you." She finds all this very odd, but figures it's harmless, and the guy is paying. The sex is fantastic. She is bounced all over the room by the energetic German, all the time honking on the duck caller. The climax is the most sensational she has ever experienced, and it is several minutes before she has recovered her breath. Finally she gasps "That was totally amazing... what do you call that? "Ah", says the German, "Four-sprung duck technique!"