Why two requests are displayed in Fiddler2 when first request sent to BlazeDS using RemoteObject of Flex

Why are two requests displayed in Fiddler2 when first request sent to BlazeDS using RemoteObject of Flex.

I use this 开发者_C百科enviroment:

• Flex SDK 3.5
• BlazeDS 4.0.1
• Spring 3.0.5
• Spring BlazeDS Integration 1.0.3

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Is the first request an OPTIONS or HEAD request?