Wierd sayings

[Cyclefrance]

We were just discussing some of the stranger sayings we have (in UK which perhaps have travelled to the USA), such as;

'I know that place like the back of my hand' - when very few of us know the backs of our hands that well, and where would such a saying have come from anyway??

Equally 'that would be like teaching your granny to suck eggs' - did granny suck eggs? Is it some obsure reference to her absence of teeth thereby rendering egg consumption a sucking affair???

All very confusing.

Any suggestions as to their derivation? Any more that confuse?

A sure sign it's Friday and winding down time....