THE MOON IS A SHARK

The upper part of the crescent in the Claire de la Lune bottle is separated by water from the lower part.

The part of the crescent above the water highly resembles a shark fin surfacing from the water (we already know thanks to the director of 4.1 that sharks are one of the main themes of s4).

(Screenshot of His Last Vow vs Behind the scenes from 4.1)





MARY AS THE SHARK

Claire de la Lune being Mary’s perfume seems to indicate a tie between Mary and the shark theme, possibly with her being the shark herself.







2 FINS = 1 CRESCENT

If the upper part of the crescent is meant to be a shark fin above the water, the lower par of the moon could actually represent the fin reflected in the water.

So the shark might be in fact comprised by two people.

These would reprise the hybrid them from Doctor who’s series 9 (such references are very probable and already frequent, read Predictions based on Doctor Who).

Since the moon is composed by a fin and its reflection, this hybrid might be comprised by two character that mirror each other (either by being similar or by being both similar and opposite).



This metaphor could also expand to the duality of the Moon, since there is a light and a dark side.

One example of two characters that would fit this description could be Sherlock and Mary.



As Redbeard too could possibly be an hybrid formed by two people (Red + Beard), the shark could possibly be the same set of characters.





THE MOON AND SHARKS IN DOCTOR WHO

As @jenna221b​ pointed out here, there are flying sharks in Doctor Who’s A Christmass Carol, written by Moffat, who specified that sharks were a particular fear of his childhood.

In two occasion in particular there is also:

Fish flying around a moon shape.



A shark going through a moon shape (the door frame has a full-moon shape and the door panel has a crescent shape).







There are also two other ties to the moon:

The character that sings to the shark is also presented with a moon shape.



This episode takes place during Amy and Rory’s honeymoon.



There is a reference to a moon which is not an actual moon but is carnivorous:

THE DOCTOR: Well, there’s a moon that’s made of actual honey. Well, not actual honey, and it’s not actually a moon, and technically it’s alive, and a bit carnivorous, but there are some lovely views.







In Doctor Who’s Kill The Moon, not written by Moffat, but possibly influenced by him, since he was showrunner, it is revealed that the Moon is actually a flying monster with fin-like parts, a concept akin to A Christmas Carol’s sharks.





So it could be that Moon and sharks is an association already in Moffat’s mind.