a dildo is like a penis but without the man attached, they come in a variety of sizes and shapes and are mainly for having something in the vagina/anus while masturbating, or if the feeling of DP is desired without the extra person. they're also good for strap on sex, or any other time when you wish you had a penis around but don't. so if you've already had a good orgasm, but she's wanting more, you could pleasure her with a dildo. i have a really nice dildo with a vibrator inside (that can come out) so i have the best of three worlds- vibrator, dildo (sleeve plus vibrator without turning it on) and vibrator. it's quite nice
These are dildos:
http://www.stockroom.com/dildos.htm
These are vibrators:
http://www.stockroom.com/vibrators.htm
like it has been said, really no difference ceptin one comes with electricity and one doesn't! I say, get a silicone dildo if you're looking into one, silicone is very nice, feels good, holds lube well, is non-pourous so it can be sterilized easily (put it in the dishwasher, top rack), can be heated in hot water or cooled in the fridge, and causes no allergic reatctions like vinyl or plastic can. only drawback with a silicone dildo is that you can't use it with silicone based lubes because the lube will eat away at the silicone of the dildo. Love you dilldo and it will love you back!

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Sage knows our mythic history, King Arthur's and Sir Caradoc's
She answers hard acrostics, has a pretty taste for paradox
She quotes in elegiacs all the crimes of Heliogabalus
In conics she can floor peculiarities parabolous
-C'hi