These are called aborts.

Not all the fruits (yes, mushrooms are called fruits) have a success in life.

Some are just not to make it until maturity and they die out before dropping there spores (see image)

Mushroom aborts are not growing and stay small and shrivled

These fruits should be removed before soaking the substrate for the next flush.

There is a discussion that aborts (per gram) might be more potent than successful fruits.

We leave that up to you to decide (or to decide not to decide).