They're some kind of government science thing..
A bio-computer or something.
Together they're super intelligent..
Alone, they turn into smart, hyperactive, attention deficit squirrels.
“She'd become a governess. It was one of the few jobs a known lady could do. And she'd taken to it well. She'd sworn that if she did indeed ever find herself dancing on rooftops with chimney sweeps she'd beat herself to death with her own umbrella.”
― Hogfather