Unexpected egg sacs appeared in tank?!

[VforVienetta]

Any idea what these might be? I spotted them in my friends tank today, all her fish are live bearing (guppies etc) so is very confused!
She has one single cleaner fish, so no chance it’s from it. I suggested they looked like a dogfish relative sac.
Bit of a snail problem, but has a hunting snail on the case.

Suggestions appreciated!

Question answered already! They’re Assassin Snail eggs.

Are you talking about the square eggs? I didn’t realise assassins could lay eggs. I’ve just introduced some to my tank to deal with a pest problem- will I ended up with 100s of assassins instead?

Yes mishfish they're the little square green sacs with white egg dots in the centre.

The fish have eaten a fair few of the eggs in my friend's tank, but she's spotted a third adult, having only bought two, so they're definitely breeding!

According to the internet, the baby snails mature in the gravel substrate, so won't be seen for a few months.