Possible Clues:

• Stagger from the counter
• Time to face creature, semi-aquatic adder?
• Perhaps it's the adder that's not 11 across
• Adder has no feet, so it can hardly walk
• He will just about make it to the total
• Might it be an adder that's beginning to fall for this?
• One might add up to getting near the fall
• Almost fall for an adder-upper
• An adder upper might be about to fall for this
• Move unsteadily; be about to fall