Certain words or phrases are commonly used as placeholders to count out a time of about one second, especially in games. This practice is formally documented from at least as early as 1960:
Since it is difficult to see a watch in a photographic darkroom, some photographers have learned to measure time in seconds by counting at their normal conversational rate but interspersing a long word between numbers, as "Mississippi one, Mississippi two, Mississippi three..." - Physical Science Study Committee, Physics (1960), p. 20.
Spencer McCain hiked the football to himself and dropped back. Four boys went out, while four others covered. One defender stayed at the line counting alligators.
Inhale deeply and slowly through your nose into your diaphragm; that should take five to seven seconds (battleship one, battleship two, battleship three…).
"One chimpanzee, two chimpanzee, three chimpanzee, four chimpanzee." I counted right along, just as I always did, and pretty soon I almost forgot about everybody all around me, and just counted and counted and bent one finger under at the end of every minute, and it wasn't nearly so bad as I was afraid it would be.
You can measure how far away a lightning bolt is by counting aloud "One hippopotamus, two hippopotamus, three hippopotamus ..." until you hear the thunder.
1996, “Cheers & Jeers”, in Field and Stream, v 101, September, p 12:
Any reader who uses the old “One Mississippi, Two Mississippi, etc.” method to estimate distance to a storm, and doesn't get any further than a count of five to eight had better be in a safe shelter.
One one thousand, two one thousand, three one thousand. This was how they had been taught to count seconds back in third grade, and Miss Timothy, a lay teacher, had told them to put their heads on the desk and raise their hands when they thought a minute had passed.
2009, Ruth White, John D. Preston, Bipolar 101: A Practical Guide to Identifying Triggers, Managing Medications, Coping with Symptoms, and More, page 125:
Mentally count as you breathe in for five seconds: one-potato, two-potato, and so on until you get to five-potato, then blow out for five seconds, counting the same way (saying “potato” approximates a second).