Hi Lelask,
Thank you for letting us know about this.
It is correct and is supposed to be that way. It is because the word 'egg' (no article) comes from the category
Food which by default has no articles, whilst the word 'an egg' comes from the category
Objects - "A" and "An" which as an article prefix on every word.
The Picture Flash, World Flash and MultiSensory sessions are designed containing pictures / words from a number of different categories. It just so happened 'an egg' and 'egg' were both contained in a session together.
I hope this information helps