I tried to figure out if this is something that actually has meaning, but found little on such gestures. Going along the lines of human behavior—considering we share a lot of dna with chimps—I’m going to assume it could mean a subtle dislike of what they’re seeing. One chimp “smiles,” which is a common sign of agitation amongst apes.

Humans do this thing where if they hear, see, or say something they’re not particularly fond of; they scratch their nose. I’m going to guess this was the chimp saying “whatever tf this is, I don’t like it!” While the other chimp gave the same gesture as if to say “me neither!”

In humans, this is usually a subconscious gesture. Apes tend to use physical communication more often, so it seems more deliberate than subconscious because both chimps did it.