What's the difference between sarcasm and having a dry sense of humor?

I've been told that my sense of humor is dry--which is not necessarily a bad thing...I think. But, I was wondering: What IS the difference between being sarcastic and having a dry sense of humor? Aren't most sarcastic remarks said dryly (without a change in the tone of voice)?
 
Funny cuz I'm told I'm sarcastic...I'm guessing with sarcasm u can tell the person is being sarcastic but with dry humor it seems kinda serious and said with more of a straight face..maybe the person doesn't know if they should laugh or not...that's my guess ^_^ hope it helps
 
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