A baby’s first laugh is a magic moment. Parents have no trouble remembering it even years later. Happening anywhere from a few weeks old to 4 or 5 months, those early laugh will very likely be small and subtle, a light and breathy chuckle. A tiny baby cannot coordinate the rapid contractions of the intercostal chest muscles required to laugh properly but the sound is unmistakable nonetheless.

For Aristotle the first time we laugh marks the instant when our soul enters our body and the moment we become truly human. He thought that laughter was what separates us from the animals. He was wrong, of course. Other animals can and do laugh and the boundary between us and other species is a matter of degree, a question of genes and culture. As for the soul, nowadays we would probably call that consciousness and we understand that it dawns slowly.

But a baby’s first laugh is a very special event and one that feels transformative. Sometimes it is a spontaneous sound of wellbeing and satisfaction. I am warm and happy and full of mother’s milk. Sometimes it is a response to something the baby sees, like a shadow waving on the wall. Best of all is when it is the result of something a parent does; returning to the room or planting a ticklish kiss. However small that first ever laugh may be, parents will recognize in it the idea that “a laugh is a smile that burst”. It is the first time that a baby expresses their absolute delight with the world.

It is a memory that can stay with you forever. When I ran my baby laughter survey one parent, Mary, took the trouble to write and tell me about “the sound of the Angels” that burst forth when she kissed her tiny daughter’s tummy. It had happened forty-two years previously but it still echoed in her memory and made her “smile with JOY”. It was one of many similar stories. This is rather remarkable given that adult memory is usually very vague and non-specific. What did you have for lunch yesterday or do on your last birthday? Not many events in our grown up lives stick like that. Even wedding days become hazy. But first laughs, first steps, first words remain with us and raise a smile decades later.

Memories of first smiles can be more elusive and uncertain. In my survey first smiles are reported anywhere from the first day to the sixth month. On top of this, parents have a harder time pinpointing the first smile and more difficulty recalling it. There are several things happening here. Not only are first smiles more subtle and fleeting but very often parents have been taught to doubt their own judgements.

There is a much repeated myth that all smiles before about six weeks are actually trapped wind or the sign of a baby filling their nappy. This myth is widespread and persistent. I’ve even seen it on large midwifing websites. But it is one that I completely reject. Many parents I’ve surveyed are convinced they have seen genuine smiles from very early on and I believe them. They are, no doubt, slightly biased but they are also studying their own baby far more intently than anyone. We will see later in the chapter why there are excellent grounds for believing they are correct. For the moment, I think it is simple enough to let parents trust their own judgement on this.

Let’s take another look at those first smiles. Yes, babies can pull funny faces when burping up milk or filling nappies. But they are equally capable of showing genuine emotion. No one doubts that first cries and first tears are real. A baby in distress is obvious to all. It seems strange that experts would want to deny that early positive emotions are also valid; that first smiles aren’t “proper smiles”.

Worse yet, here we have new parents, uncertain of their own abilities, being told by experts that they are wrong about something so basic. It is not a great way to start. The main message of this book is that between you and your baby you will figure most things out for yourselves. Nobody is ever properly prepared for a baby. But equally, you know more than you realise and will learn fast. It’s even more stressful and bewildering for the baby but their little laughs and smiles are a sign they are succeeding. No one should take that away from them.

There is another milestone for new mothers that it is often overlooked. When was the first time your baby made you laugh? This was earlier than you think. Of course, there can be big smiles at the very beginning. Perhaps the time when you first suspected a baby was to be expected? Perhaps when it was confirmed by that second blue line on a pregnancy test? Or maybe a little later when seeing another mum with her new baby made the reality of your own future more concrete?

But I am not talking about those moments. I like to think that the first time your baby directly makes you laugh is when something about their wriggling inside you makes you smile or starts you giggling. A good friend tells me of laughing when feeling that her unborn daughter had got the hiccups. In her memoir of her pregnancy, Chitra Ramaswamy describes going out for dinner with friends to celebrate her birthday. Five months pregnant she can’t enjoy the adventurous food of the restaurant and is distracted from her friends as her baby put on ‘furtive firework display’ just for her. That private joy became one of the happiest moments of her life.

Better yet, your baby might be laughing along with you. Anecdotal reports of babies pictured smiling in ultrasounds have been around since 2000, when the resolution of scans became good enough to show facial expressions. Looking at this evidence systematically, the psychologist Nadja Reissland at the University of Durham and colleagues have identified seven foetal facial expressions and confirmed that both crying and laughing are ‘practiced’ in the womb.