Who/what/when/where/how/why can I share my answers?

Question

I've notice that sometimes I can tweet my SO answers.

Something like

shows up by my answer.

• Who se answers can I share?
• What was I thinking when I decided that the who/what/when... theme was a good idea?
• When does this happen? It looks like I can only share my answer for a short time after I post it.
• Where do the tweets/shares go in the series of pipes and tubes?
• How lame is this bullet point?
• Why does this happen? Does the answer have to get upvotes? Are all answers share-able?

Answer 1

This only appears:

• a random percent of the time, decreasing chance with greater reputation
• on your posts
• if they are greater than 400 characters in length
• for 1 hour after posting