In the fourth episode, when Debbie receives "literally a thousand thank-yous" from three blue-skinned guys, they speak in unison and then, when they finish, one of them adds an extra "thank you". It may seem like he's just being The Slow One - until you realise that if you divide 1000 thank-yous between three people one of them will indeed end up with one more thank-you than others...
In the Season 1 finale, Debbie fails to recognise Negatus. To be fair, one sixth of the population of Yonderland looks exactly like him.
Fridge Logic:
Elf evidently has no idea how to work various household cleaning appliances, including a vacuum. A throwaway line from Negatus reveals there are vacuum cleaners in Yonderland, making Elf's ineptitude slightly less credible.
Although out of all the appliances, the vacuum cleaner is actually the one that Elf has the least trouble understanding both how to use and what it's meant to be used for. And just because Yonderland apparently has vacuum cleaners, who's to say that Elf specifically has ever used one or that they work/look the same as ours in the first place..?
