Twitching is used to help subdue horses and avoid using drugs. Twitching the upper lip causes endorphins that kick in as soon as the twitch is activated and subside once the twitch is removed without any sedative effect. An alternative method involves twitching the ear which likely involves fear or stress compared to lip twitching.
… the use of a nose twitch could be endorsed, but an ear twitch should not be condoned.” – Sue Dyson, Vet MB PhD
Source: The Paulick Report, May 29, 2023. Link.