Clue number two was quite an easy one, as it really looks like a chocolate Easter egg!
This set is actually titled "British Birds Eggs" on the fronts of the cards, but "Birds Eggs" on the backs, and they are cleverly numbered to match up with the birds in set O100-414 : O/2-95 : O/47 ("British Birds" first series 1905/6, also issued by Imperial Tobacco Co.) The idea with this was so you could display the bird cards on the top or bottom row of your slip in album and the eggs on the row directly above or below.
The fronts of our set are lithographed in colour and the backs in green, with a descriptive text. They must have either been reprinted at some stage or the availability of the card used altered, as they can be found on (a) white board with semi-glossy backs, or (b) off white board with matt backs. Strangely these two different boards also occur in the set of "British Birds" which makes me wonder if when the birds were issued the set of eggs were reissued.
By the way, Ogdens also issued a second series of "British Birds" in 1908, these were numbered 51-100. Sadly no egg cards were produced to match them.
This set is sometimes confused with another Ogden's Ltd "Birds Eggs" (O100-476 : O/2-128 : O/35 - 1923). It may have the same title, and green descriptive backs, but the 1923 version are cut out cards, with a perforation around the egg to allow it to stand proud whilst the rest of the card is pulled slightly backwards. And once again, in 1923, there was a cut-out set of "British Birds" (O100-482 : 02/131 : O/49) with the numbers matching so the two sets could form a pair in a slot in album.
Both of these later sets were also issued by Imperial Tobacco Co of Canada.
It was reported in our original Ogden reference book (RB.15) that cards of the 1923 series existed which had "cut" in the centre of the back rather than "push". They presumed these to be an export issue. However the only other mention of this in either of the World Indexes is in the most recent which says "uncut cards are known". In the dark recesses of my mind is something about not allowing pre-perforated cards to be exported. And it does say "uncut cards are known" against the eggs, the birds, and with "Children of All Nations", so perhaps in these cases the collector had to make their own cut out fold down cards, and instructions were given on the packet? Do let us know if you can tell us more