I popped next door yesterday afternoon to post an envelope through our neighbours' door. (I donate to their daughter's 'sheep sanctuary' from time to time.) They have three super cats. The eldest ('Tiger Lily') was sitting in their window, watching me and smiling.
Sadly, their letterbox is rather fierce, and I got my hand trapped in it. Nobody was in, and I tugged & tugged, trying to free it. Tiger Lily watched with great interest, and I swear she was actually laughing!
I envisaged spending the rest of the day with one hand poking in through their front door, but fortunately I eventually extricated myself.
Tiger Lily looked a trifle disappointed!
Honestly, cats do actually smile and laugh if one understands their body language and facial expressions.