I'd love to be one of a pair of conjoined twins filling the form in. "I think I share two feet, but my sister says we have one each."
Being a bit more serious for a moment, I know they try to make these forms straightforward, albeit not always mapping on properly to eligibility criteria, but I can't help but think of scenarios that don't fit rigid prescribed lists, and it doesn't help where, in my opinion, the eligibility criteria for benefits are bonkers.
Still, we have to humour the politicians and senior bureaucrats. It occurs to me that next time I fill a PIP form in, I'll conceptualise it in terms of teaching a primary school child.