you could have a hatchling ringneck snake in there, they usually stay under 4 inches till they're about a year old, at which point he'd need a bigger tank, thus freeing the 2.5 up for another new project.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)