I found 2 short fat squirming worms on the top of the bedding. After close inspection, they look like just the tail end of red worms. Then I found one with the tail end cut-off (dunno if it matches with one of the tails). What could have done such a horrible thing? Any thoughts?

I'm just curious, because there are still plenty of worms in the bin and I don't feel there's a need to worry.