Very familiar
It's like you're looking into my toilet. I see these all the time. My best guess is ascaris. My theory is that it's the outer skins that pass and not the whole worm, rather torn up from the colon breaking things down. I used to post about seeing "cappellini"-like worms (for anyone who may not know, capellini is super thin spaghetti-like pasta). I have since come to theorize that they are probably
Ascaris - not plump and whitish like the heaps found in gallery photos, but broken down and semi-digested.
I did get one of those huge plump, white ones in my toilet once after a heavy-handed day of parasite-slaying. It scared the behookas out of me. Because of the evidence of this type of worm (ascaris), I now have the theory that what I see so often is just more of the same, but again, broken down. Where there is one, there must be others...
I have another theory - only the outer skins remain because the insides get eaten up by other types of parasites. Which begs of another question: do
parasites eat each other after death?
One more thing: the "lump" in the picture that you refer to as a fluke - try poking at it with a plastic knife or other such instrument. You may see, as I often do, that it's actually just more ascaris. When it breaks apart, long thin strands become evident.