Noticing Stephen's puzzlement, he wrote, This is a device that records images. Might not work though.

The first egg was beginning to hatch and he nearly dropped the notebook in his haste to take notes on what was happening. The translucent shell peeled back and the tiny green creature popped out, its body also slightly translucent. Its horns were mere buds, but its fingers were as long and savagely clawed as an adult's.

More of the little beasts were hatching, and now the two scientists had a melancholy glimpse of what newborn grindylow ate: each other. Lupin made a face as the babies fell on each other until there were only three left. The biggest of the three took it upon itself to eat the remaining unhatched eggs, as well.

Survival of the fittest, he wrote to Stephen, no doubt introducing him to the concept for the first time.