Ice cream — Food safety facts
Feed with care · Cats · full breakdown on the linked food page
Lactose, sugar and fat — most pets get diarrhoea. Check for xylitol and chocolate, which are toxic.
Short answer
A tiny spoonful of ice cream is not an emergency for a cat. Ice cream contains lactose, sugar and fat, which can often cause loose stools in cats. Watch for vomiting, diarrhea, or any signs of stomach upset. If any of those appear, give your vet a call.