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Starting at about ten seconds into this video of the SpaceX CRS-19 launch:

One can observe what looks something like a rat moving around the side of the second-stage rocket nozzle.

How can this observation be explained?

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    $\begingroup$ "Godspeed, Spacerat." $\endgroup$ Jan 29, 2021 at 4:31
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    $\begingroup$ pareidolia wins again $\endgroup$ Jan 29, 2021 at 13:13
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    $\begingroup$ Have these guys ever seen a rat, or watched a rat move? looks more like Fingermouse to me. $\endgroup$
    – user20636
    Jan 30, 2021 at 11:57
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    $\begingroup$ Rats! or in this case, lack thereof; the video link is no longer working. $\endgroup$
    – uhoh
    Jul 23, 2021 at 1:28
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    $\begingroup$ @uhoh I believe this is the relevant video.. youtube.com/watch?v=fciqfVXAr7I $\endgroup$ Jul 23, 2021 at 11:53

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I think we can safely rule out a live rat at second-stage altitudes.

The most likely explanation is that the "rat" is made up of chips of oxygen ice, as described here, caught against the crescent-shaped manifold wrapped around the upper part of the nozzle.

Under the acceleration of the rocket, the path along the narrowing crescent, in the direction the "rat" moves, is slightly "downhill". An object caught there would bounce around slightly with the vibration of the engine, and at some point could start migrating down along the arc of the manifold.

Incidentally, in the absence of much, much more evidence, suggestions that this is a live rat on a filming set at low altitude, and that SpaceX's launch videos are faked, are not credible to me. Commercial, profit-driven corporations appear to give SpaceX a great deal of money to put expensive things into orbit. If you want me to believe that's not what's going on, the explanation needs to be simpler than my bouncing debris hypothesis.

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    $\begingroup$ Mars rat had to get home somehow space.com/21396-mars-rat-curiosity-rover-photo.html $\endgroup$ Jan 29, 2021 at 4:56
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    $\begingroup$ If this is ice, you don't need "bouncing slightly" for it to move. The nozzle will be extremely hot, so Leidenfrost effect - a microscopic layer of steam forming between the ice and the hot metal - will make its motion near-perfectly frictionless, So any tiny changes in angle of the acceleration will make the ice slide freely with no resistance. $\endgroup$
    – SF.
    Jan 29, 2021 at 12:01
  • $\begingroup$ @SF. or the "cat on a hot tin roof" effect, though I guess it 's the "cat on a hot metal nozzle chasing a rat who is trying to get back to Mars" effect in this case. $\endgroup$
    – uhoh
    Feb 6, 2021 at 14:07
  • $\begingroup$ it's obviously ice. $\endgroup$ Feb 10, 2021 at 8:29

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