Each old-timey doctor represents a transformation on a string. You are supposed to figure them out by INFERENCE.
This doctor deletes the first two letters and the last two letters of the input, e.g., SPLENDOR > LEND.
This doctor interprets the first two letters of the input as the symbol for a chemical element, and outputs the name of that element, e.g., AGRICULTURE > SILVER.
This doctor reverses the letters in a word, e.g., KEEP > PEEK.
This doctor adds a Y to the end of the input, e.g., BUS > BUSY.
This doctor swaps the last letter of the input with the penultimate letter, e.g., CANDIED > CANDIDE.
This doctor translates the input into French, e.g., LEG > JAMBE.
With all these rules in place, the final transformation is this: TETRAPOD gets the top and bottom cut off to become TRAP gets reversed to become PART gets a Y added to become PARTY gets translated into French to become FETE gets its last two letters swapped to become FEET, which is the answer.