I've always assumed it was "on" but if you consult Ms Google, she says it can be either!
Hi Pen,
It is quite common for idioms and other common expressions to have variations.
The tongue-twister that I have been struggling with picturing for the last couple of days is a case in point. Is
What noise annoys an oyster most? A noisy noise an oyster most. the better variation or should I use
Any noise annoys an oyster but a noisy noise annoys an oyster more.
By the time, I had worked out how to picture either, I decided it was too complicated to make a good rebus and I gave it the flick and so you will have to put up with a rather weak joke. Not a match for your excellent rebus.
3 11(#4 #3 #3 1) 10(#2 #5 #3) #5 #3 6(#3 #3)
Conceptually one line.
The d Picture 1. Plural abbreviation.
Picture 2. Two words. You need the second.
Picture 3. Past tense. Make homophone.
Copied from Pen’s last rebus.
Picture 4. The alternating abbreviation.
Picture 5. Two words. You need the first.
Picture 7. Make Anagram.
Picture 8. (4 letters) Make Homophone
Picture 9. First name of the taller one.
Picture 10. The object not the action. Make Homophone of the last word.
I came across this photo of our first Border Collie, Bessie (1985-1998).