Not my cat (long story) has fleas. I've just accidentally used the under 4kg one instead of the over 4kg. Will it still do something? It's advantage spot on, my cat reacts to it so I had some spare!
Without weighing him I'm not sure if his exact weight but I suspect he is hefty over 4kg
(Before anyone asks, no I'm not kidnapping him, yes I flea treat him because he is crawling with them) 