Treacherous road like fresh mushroom?

In the comedy Murder by Death (1976), Peter Sellers plays detective Sidney Wang who has some great lines including:

“Questions like athlete’s foot. After while, very irritating.”
“Conversation like television set on honeymoon: unnecessary.”

He gets interrupted in the middle of:

“Treacherous road like fresh mushroom, must always…”

Must always what??? Any ideas on how to complete this?

X.0.4
Questions are a burden to others, answers a prison for oneself.