Perseid meteor - spiral burnout

Canon EOS 50D, hooded Sigma EF-S 30mm ƒ/1.4 EX DC HSM prime @ ƒ/2.8, ISO 100, 30 sec. exposure, tripod. See this shot for entire image.

You can see regular spiral pulsing in the trail, especially in the full size version (click "All Sizes" above the image); I think this may be the result of friction induced tumbling. The shot went on for about ten seconds past the time the trail disappeared, so that bottom section is the final burnout.