In the book The Island of Dr. Moreau, there is a description of the beast creatures not being able to laugh. In describing the strange characteristics of the beast people, the main character states "None could laugh, though the Ape Man had a chattering titter.) (Pg. 119 in the large type edition)

Then on pg. 126, the main character, Prendick, said about the beast people "Then they spoke inaudible things, and I heard the Satyr laughing.

Pg. 135 says "The Hyena-Swine still ran close to me, watching me as it ran, every now and then puckering it's muzzle with a snarling laugh."

And finally pg. 136 says "...and the Hyena-Swine ran, laughing savagely, by my side."

So, this was definitely a slip-up on Wells' part. It would've been fine if he never said they couldn't laugh. But I thought that was an interesting difference between us and the beasts, that we were able to laugh. So it really stuck out when all those other times the creatures were laughing.