That's definitely his 'serious something really cool' mode...

[He's so afraid to hope for this one. It's such a personal thing, something from their old lives. A memory. He carefully twists open the top and lifts it up to see the jar full of loose leaves and some other things mixed with it. He leans it close to smell and-]

Ohmigosh it's real. [Leo holds it up to his shoulder for Casey to smell.] Smell that- don't take a big whiff. Just a little sniff.