There are occasions when I stay silent simply because I dont feel like putting the energy into being personable. More often, however, it's a matter of not knowing what to say (ie: failing to be reciprocal in conversation), not being able to break into the conversation, not being able to start a conversation, or in the worst case being simply unable to speak (mutism caused by stress). Once I start, though, it can be pretty hard to make me stop.
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What would Flying Spaghetti Monster do?