The latest episode of The Big Bang Theory reminded us just how great Sheldon and Penny are together. Here are some of our favorite moments!

Last week’s episode, “The Intimacy Acceleration,” saw Penny and Sheldon gamely try an experiment which claimed to have its subjects fall in love in mere hours. Though the experiment failed in terms of romantic love, taking the test reminded Sheldon and Penny – and the audience – of their adorably familial relationship.

So here are a few of the sweetest (and funniest) of this mis-matched pair’s awesome escapades.

The original Soft Kitty

This bizarre little lullaby has become a staple of The Big Bang Theory, and its attendant merchandise. But first came the vapo-rub, and one of Penny’s earliest moments of tenderness for Sheldon.

Sheldon sings Soft Kitty to Penny

And of course, Soft Kitty only got better with time. Reciprocity is the mother of fondness (or something) and Sheldon capped off an episode of caring for Penny with the adorable anthem.

The Leonard Nemoy napkin

In what became a television moment for the ages (and especially poignant in light of Mr. Nemoy’s recent passing) Penny’s small, thoughtful Christmas present to Sheldon sent Dr. Cooper through the roof with joy. So much so, that he touched someone else.

Penny probes Sheldon about Amy

Though not exclusively a Penny and Sheldon thing, we love this moment because Sheldon chooses to answer Penny’s questions. It’s a monumental admission from the scientist, but its only made possible by the closeness he feels with Penny.

Penny and Sheldon tell their secrets

Though this clip is a little bit insult-heavy (which is kind of how Sheldon and Penny roll) we still love it for the confessional moments between the two. Honesty, apologies, a great big hug? It all just shows how far both characters have come.

The Big Bang Theory season 8, episode 17, “The Colonization Application,” airs on Thursday, March 5 at 8:00 p.m. on CBS.

What are your favorite Sheldon/Penny moments on ‘The Big Bang Theory’?