I just realized that Mrs. Hudson turned to look at John. Then she turned back around and kept walking towards the cabbie.

At first I was trying to calculate where exactly Sherlock was on the sidelines - and gathered enough information to pinpoint his spot. Which is around where Mrs. Hudson’s placement is now [just a tad bit farther to the left of course, out of camera range].

Then I began to wonder…

Did Mrs. Hudson see Sherlock?

But no, if she had seen him - she would have been yelling up and down, calling for John, etc. So then…

Was Mrs. Hudson in on his plan also?

Maybe I’m over-deducing along with too much chocolate and it being almost midnight.