Bob has, in fact, finished eating his slice of pizza – at first hanging out of his mouth like an oversized floppy greasy sort of cigar, when Mo walks in – before he manages to notice her.

It's not until he's done something involving a pixelated explosion, and crowed out "See, that is how you frag someone!" before turning around – presumably expecting to see Peter-Fred or Claire – that he notices Mo, come to think of it.

And then he blinks at her, as his brain switches processing centers. Slowly.