I recall an interview with him in which he said he sang the theme to the 1989 Batman movie into a tape recorder. The reason was, he thought of it during a comme

I recall an interview with him in which he said he sang the theme to the 1989 Batman movie into a tape recorder. The reason was, he thought of it during a commercial airline flight and didn't want to forget it. According to the interview, he went into the restroom and sang it into his tape recorder as loud as possible in order to be heard over the plane noise. That story or one like it is probably where the notion comes from.