music: Song: Name The Artist: Thorn In My Side?

Questions

What part of a bathroom tap most often needs to be replaced?

What part of a camera clicks when a photograph is taken?

What part of a face, according to research, do infants like most to look at?

What part of a horse would you look at to determine its age?

What part of a person's body must be clutched to feel the 'biceps'?