While they might look like normal little people – well, within reason – the differences between babies and us comprise a great deal more than simply size. When they’re born, our baby’s five senses are far from fully developed, and though we might swear blind that our little one is watching the TV, odds are she’s simply gazing in that direction while wondering why that odd person beside her is getting all excited over nothing. In fact, their sensory development is quite different to what you might think.

Surprisingly, a newborn’s most acute sense is that of smell, and experiments on babies show they’re able to distinguish between their mother’s milk and that of another woman by smell alone. That’s pretty impressive, considering that no matter how many times I smell milk from the fridge, I can never tell if it’s gone off until a big lump of congealed yuck drops into my cereal.

According to the experts, touch is also a key sense at this stage. A newborn’s hands and mouths are their most sensitive parts, while the rest of the body can feel temperature and pain, before beginning to sense pressure and touch. Before you know it, that fabric softener you’ve been using doesn’t make things soft enough for her highness, and you’ll need to fork out on one that’s three times the price.

She can hear, but not all the frequencies and volumes we can – if you whisper sweet, soothing words in her ear, she might not even know you’re there. Her tastebuds can only distinguish between sweet, salty, sour and bitter tastes, and despite a persistent myth that this is all anyone can taste, she’ll develop the full range of tastes later. And her vision is probably the least developed of all.

Newborn babies can see around twelve inches and in very limited colours, only able to sharply discern high contrast patterns, such as a chessboard – though why they’d be staring at a chessboard from a distance of twelve inches is anybody’s guess. Beyond that, the world is a blurry mess of movement and shapes and it’s not until around four months, when she develops binocular vision, that she can tell how near or far an object is, its size and relative dimensions, and thus be able to reach out and touch it. Prior to that, no matter how many times she punches you in the mouth, you can’t attribute intention to her – it’s just luck that her flailing hand caught you six times a day in the exact same spot.

There are other senses beyond the five we are (wrongly) taught at school. If we class a sense as a bunch of cells designed to pick up on a specific input, then most experts believe we have at least nine, and maybe as many as twenty-one, including hunger, thirst, balance (which enables us to sense movement), the sense we need to pee or poop, and a sense of the passage of time. In fact, most experts divide the sense of touch into different, discrete categories: touch, pressure, temperature, pain, and itch. So that’s an awful lot of different body systems for our babies to physiologically develop and learn to process.

But if babies are stuck in a bubble with limited perception of the world around them, then how on earth is it that Izzie manages to time her indiscretions for the worst possible time? Her sense of inconvenient timing arrived at birth and has been developing ever since. She’s fast asleep, the light is off, but the second – literally the very second – your head hits the pillow, she starts to cry. You cook dinner and she doesn’t make a murmur, but the moment you sit down to eat and you insert your fork into that first precious potato she somehow senses that now’s the time to scream. Telephone call? I’m going to cry. Furthest point of the walk from the car? I’m going to choose this exact moment to poop.

This morning she somehow timed her pee to the exact second I was slipping the clean nappy into place over the top of the dirty one – the precise moment my hand was positioned beneath her where she could give it a shower. A heartbeat of a chance and she took it. And what’s more, I have a tiny cut on that hand from where she scratched me. I learned two things: baby urine is surprisingly hot, and it feels oddly like acid on an open wound. And a third thing: it’s uncanny how awkward Izzie’s timing can be.

The worst is with her nappies. I have realised, since Izzie was born, that I’m rather squeamish. I don’t understand quite how or when it happened. When I was working as a care assistant in an old people’s home, and later as a student nurse on an infection control ward, I used to roll my eyes when I heard parents moan about dirty nappies. I made a living from wiping bottoms, and not just any old bottoms, but people with clostridium difficile, a hospital superbug that makes people incontinent and their poop into orange marmalade. I cleaned up diarrhoea after people had been eating sweetcorn. On one memorable occasion, we had to hoist a guy with a gangrenous sacral pressure sore up off the bed so he could poop into my (gloved) hands, which is the closest I’ve come to vomiting on a job.

The point is, I did these things without blinking. Perhaps I repressed my disgust and now it’s coming back to bite me, but somehow Izzie seems to know when I’m alone with her, and stores up her poop for then. And this isn’t just any old poop. Since starting her on the Comfort milk, it’s green and it reeks like a diseased goose.

It follows a pattern these days. First, the hard nugget that lures you onto the changing table with a peg on your nose. Then, as you remove the nappy, she passes a softer stool that comes out like a sausage and coils round and round until you have a twelve-inch Cumberland you have to detach from her bottom with a piece of tissue. Then she waits until you’ve been pulled into thinking she’s finished before she projects a green stream of mushy peas across the back of your hand.

Every time, nugget, sausage, peas. Every time I change her, that is. When her mother changes her, there’s none of that, and her mother has no sense of smell. It’s like she senses my weakness and goes in for the kill. So if there are any experts reading this, you need to add a new sense to your list: a baby’s sense of inconvenient timing.