Mixed metaphor

When one or both of the terms can only be consciously metaphorical. Little warning is needed against it; it is so conspicuous as seldom to get into speech or print unexpected. This is not the time to throw up the sponge, when the enemy, already weakened and divided, are on the run to a new defensive position. A mixture of the prize-ring and battlefield. / The Rt. Hon. Gentleman is leading the people over the precipice with his head in the sand. A strange confusion between the behaviour of Gadarene swine and that of ostriches. / There is every indication that Nigeria will be a tower of strength and will forge ahead. A mixture of a fortress and a ship. / The Avon and Dorset River Board should not act like King Canute, bury its head in the sands, and ride rough-shod over the interests of those who live by the land and enjoy their fishing. A picture that staggers the imagination, and a libel on a great king.

In the following extract from a speech it is difficult to be sure how many times metaphors are mixed; readers versed in the mysteries of oscillation may be able to decide: No society, no community, can place its house in such a condition that it is always on a rock, oscillating between solvency and insolvency. What I have to do is to see that our house is built upon a solid foundation, never allowing the possibility of the Society's lifeblood being sapped. Just in proportion as you are careful in looking after the condition of your income, just in proportion as you deal with them carefully, will the solidarity of the Society's financial condition remain intact. Immediately you begin to play fast and loose with your income the first blow at your financial stability will have been struck.

H.W. Fowler
A Dictionary of Modern English Usage
2nd Edition

Here are some examples of zeugmatic mixed metaphors:

• You're barking up the wrong end of the stick.
• It's no skin off a duck's back.
• That's a different kettle of red herrings.
• opening Pandora's can of worms
• moving the goal posts on a level playing field
• Don't count all the eggs in one basket until the chickens have hatched
• having a different kettle on the fire
• enough rope to shoot yourself in the foot
• a spanner in the ointment
• Don't rock the apple cart
• Beat around the bush with two birds in it
• As plain as the pikestaff on your face
• Snookering yourself in the foot
• Too many cooks in one basket
• A red rag to a bull in a china shop
• The thin end of the iceberg
• A finger in many dykes

Please /msg me with any more that you know, as I am collecting zeugmatic mixed metaphors -- ponder