I sure hope the anonymous thing is working! You did say "fucking bizarre", so here goes.

A bestiality fic, where someone forces poor, innocent Jensen to get fucked by a BIG dog, knot and all, with bondage. Jeff either has to watch, unable to help, or bursts in too late to stop it and has to wait until it's over tp get the dog loose. They're not involved at this point, but they get together for comfort later(Jensen's HAD the hurt).