I’m sure many of us that have predominantly ridden lesson horses over the years have met one that’s “crop sour.” The ones that will barely respond to any leg aids at all if you are not carrying a crop/whip, but as soon as you pick one up they’ll go from a halt to a nice forward canter with just a brush of your calf. No need to actually USE the crop at any time, just carrying it is enough. Put it back down, and they’re dead in the water again. The one’s I’ve met, it doesn’t seem to matter how sneaky the rider tries to be picking it up or passing it back to somebody on the ground, the horse knows if you have it or not, and it’s like holding a magic jewel of responsiveness.
The reason I ask is that my 3.5 year old greenie (backed in June, not by me) is starting to experiment with “what happens if I don’t respond to her leg?” I’m thinking a little reminding with a crop is likely to be the ticket, but I want to make sure I do everything I can to make it a temporary training aid/assist, not something his riders will need to carry to get him to move for the next 20 years.