I was thinking the same thing! There seems to be a design flaw in that brand of wormer. But I'll never do that again, lol, next time I'll squirt out everything but the exact dose before giving it to them.LOL, this has happened to many of us..... perhaps the company with those 'stops' that slip need to figure out a different way to make their wormer applicators? Yes, the very first time it happened to me, I freaked & called the vet too. She chuckled and said no problem..... and hey, the horse is not going to have any worms!!