Habituation means getting used to things - like the girth, having a rider on the back, being hosed etc. It’s important that we help horses get used to things without triggering the flight response. The flight response is stored in the brain and can easily be triggered again, so when we habituate we need to be careful of that. 

Flooding should always be avoided. This is when the horse is exposed to the scary object with no way out of the situation, and not removing the new thing until they stop reacting. This leads to increased stress and a negative affective state. 

Here are a couple of effective habituation techniques:

Gradual habituation is introducing scary things in very small steps until the horse gets used to it, without triggering the flight response.

Overshadowing means that the horse receives two or more stimuli at any one time, where one of them will overshadow the other. Through training to stop, step back and go in a controlled way while the frightening object approaches, the horse can learn to be more controlled by the signals than by the scary object. In a short time, the horse will habituate to it.

Stimulus blending means blending the thing the horse is scared of with another stimulus, for example using the radio to blend with the sound of the clippers. 

Counter conditioning is when we give the horse something he likes while also introducing something scary, for example giving the horse food during clipping. Clicker training can be used for counter conditioning. 

Approach conditioning is a powerful technique that can be used for habituation, where the scary object moves away as the horse is approaching.