Possible Clues:

• The cat sounds pleased with its turn, if you put your foot in it
• Double R? It's that you've put your foot in it
• Bit of tack - sound pleased it's returned
• Rider's footpiece
• Might one make rust rip and put one's foot in it
• It might help you get a leg up
• Even if you've put your foot in it, the cat is back with a happy sound, so it is
• A foothold on the mount
• Mix it around R and put your foot in it
• As a result of this mix-up, by the sound of it, you may put your foot in it