To save a Snap in Chat while viewing, you can...

• Press and hold on it and tap ‘Save in Chat’
• Swipe up on the Snap and tap ‘Save in Chat’ 
• Tap the save button in the bottom right corner

Only photo Snaps set to no limit, and video Snaps set to loop can be saved in Chat. Look for the timer with the ∞ icon.

After saving a Snap, the Snap will appear in the chat as Chat Media.