Deductive verification provides a proof that, under the provided pre-conditions, each terminating execution of a given function satisfies the stated post-conditions. In general, pre- and post-conditions are expressed in a logical specification language and typically rely on theories including abstract definitions, axioms and lemmas. As they are written by humans, errors may be introduced into specifications. Some errors can be detected when the proof fails, but sometimes, they remain unnoticed due to misleading proofs: most of the program may become dead code under the provided pre-conditions, or the proof may succeed because of inconsistencies in hypotheses and axioms. In this tool paper, we explore how to detect such unwanted situations by using deductive verification techniques and describe the smoke test mechanism in Frama-C/WP, a popular deductive verifier for C code. We show that, while the intuitive idea is simple, making it practical requires optimizations to scale up, and report on experiments with critical industrial code. Although our method is based on proof techniques, it is not complete and is similar to testing. In the end, can we ever be sure that our programs are proved well enough?