I think Magpie's answer was right on. I've attended from time to time a free lunchtime concert series in the city park that is frequented by a similar handicapped group. Some members like to get up and dance to the music, which is perfectly acceptable (as far as I'm concerned), as long as they don't get so close they are threatening to upset the equipment. Usually their social worker is able to maintain enough control that they don't disturb the performers. I like Big Mick's solution also.