Well,
Remember - I could very well be lowering my trousers to talk.
In this one they seem very compressed and somewhat staggered or offset.
When palpating I often feel this with follicles but, after ovulation, they get spaced out in the oviduct in much more of a single line. Compare the above with this one to see what I mean;
That pic also shows what I think might be a slug closest to the vent. It could of course be nothing at all but if it is the size difference between it and the others is what makes me think slug.
Hopefully someone with more experience can chime in and give more input.
del