So what does that look like in a dog? My family has a dog and she has a pretty nice life and is usually pretty happy, especially when upsidedown having a belly rub. Are her flailing legs and head and panting considered dog laughter?
According to research[1] whispering while playing with your dog can initiate play more reliably. This is because our whisper is closer to the frequencies of their laugh. It is even more powerful than the play-bow.
Growling is obviously a well known sign of fear and aggression but I guess the context is important.
There's also the high pitched excited yip and then the tongue out wiggling walk thing as well both of which might be laughter I think.