Quite literally, human bodies when comfortable undergo a thawing out process. Initially we start off stiff and rigid, even appearing cold. But over time we open up and become more loose, ready to take part in activities, or converse. Here is a summary of the defrosting process:

[A] Strangers meet, but keep their distance with arms and or legs crossed. Buttons and jackets are done up tight.
[B] Legs become uncrossed, but arms remained uncrossed as we decide our company is no immediate threat.
[C] Conversation is initiated, usually small talk, until a common interest is discovered. Once this happens rapport begins forming and gesticulation is used to liven up the speech. At first, the arms re-cross after speaking, but eventually they stay loose and drop to the sides or find themselves in pockets.
[D] Attire is loosened and jackets are removed.
[E] The legs become uncrossed and a foot is extended toward their company, but the back foot bears most of the weight.
[F] If rapport increases and trust builds, the space between the strangers might shrink bringing them into each others personal space zone.
[G] Touching in safe zones like the elbows and arms might solidify the relationship, but touching is not always expected or common.