"Social" yawn (is that the word for it?) DS aged 2.4 doesn't do it

[georgimama]

I don't know if there is a proper phrase for this, but you know how if someone yawns, you yawn too? Well DS doesn't. Is this normal? When does this behaviour kick in, if it is normal?

I'm sure I read that doesn't happen until later. (In a Desmond Morris book I think.)
I remember trying it with my newborn.