Touching her feverish brother's forehead, Simmi says…

Why

Simmi's hand is genuinely picking up something real — her brother's forehead does feel warmer than usual, and that instinct isn't wrong. The trouble is asking her skin to do a job it was never built for. Skin can only sense HEAT MOVING into or out of it, roughly and by feel — it cannot count degrees, and different people's hands read the exact same forehead as 'a bit warm' or 'quite hot' depending on how warm their OWN hand already is. A thermometer works completely differently: it uses a liquid or a sensor that changes by a fixed, measurable amount for every single degree, giving the same number no matter who reads it. Test: touch the same forehead right after washing your hands in cold water, then again after warm water — it will feel like a different temperature both times, though the forehead never changed. Mother is right: a hand can tell warm from not-warm, but only a thermometer can tell you the actual number.