re: something moving?
Methane rain droplets?
I'll be more conservative with my interpretations.
The Huygens spacecraft apparently caused some melting
and vaporization of the surrounding Methane snow-crust/slush,
or some similar frozen, or near-frozen hydrocarbon.
So that that brief bright glare at the lower lefthand corner may have been weak Titanian sunlight reflected off of a temporary [manmade] puddle of liquid beside the spacecraft; and some of the resulting rising Methane vapor from it may have quickly condensed into droplets onto the camera lens.