How do you tell the difference between slug eggs and old slow release fertiliser pellets ?

Last Winter I added some slow release fertiliser granules to the top of my pots , which had my bulbs in- as I am emptying them now- I can see lots of them- however most of the pop between my fingers - which made me think they may be slug eggs - will slow release fertiliser go like this in one season ? I was going to reuse this compost for my new plants with new compost and fertiliser mixed in - but now I am worried I am leaving slug eggs behind - does anyone know ?