I beg to disagree---I think we've the only animals who ever have sex for any (thought-out) reason BUT pleasure! Sure, the 'lower animals' are driven by their hormones (just like we are) but you'll NEVER catch a dog thinking, "Well, if I have sex with HIM, I bet he'd give me diamond dog-collar". (*grin*)
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Some days are easy, like licking frosting off a spoon: today was like stapling Jell-o to a brick.