When you use a magic whistle, if you have more than a certain number (3 or so) pets teleporting to your side, condense it into a single message saying “Your pets appear around you.”

Make magic whistles a charged tool. When out of charges, it behaves like a tin whistle. Its initial amount of charges and the amount it gets back by recharging are in the “high” tier like a tinning kit or camera, generating with 30-99 charges.

Increase the price of the magic whistle to 50 or 100 zorkmids. Identification of the whistle type is trivial anyway.

Applying a blessed whistle (either type) will unparalyze pets in range.

Applying a blessed magic whistle while confused teleports you to one of your pets.

Cursed magic whistles send pets away from you. (This is perhaps exploitable with e.g. purple rain strategies on Astral.)

Add spell of summon pets, a level 2 or 3 matter spell that duplicates the effects of a magic whistle. The name needs work.