spot the difference

At dinner, as usual, Liam is lagging behind everyone else...

Liam: Hey, I know! Let's play 'spot the difference'

Me: Oh, that's easy... your plate's different to everyone elses' because ours are almost empty and yours is still almost full! Come on, eat up!

Liam: No, Mammy, 'spot the difference' is not a race. Oh! But if this is a race, maybe I should eat faster then!

Me: Um, yeah... whatever...