Noticing.
This works because it takes us out of the instinctual fight/flight/freeze part of our brain into the noticing/rational part. It is much more difficult to panic if we are busy noticing things around us.
 
Try the 54321 method:

• 5 things you see
• 4 you can hear
• 3 you can touch
• 2 you can smell
• 1 you can taste