  Multi-particle states with additional pions are expected to result in a
non-negligible excited-state contamination in lattice simulations. We show that
heavy meson chiral perturbation theory can be employed to calculate the
contamination due to two-particle $B\pi$ states in various $B$-meson
observables like the $B$-meson decay constant and the $BB^*\pi$ coupling. We
work in the static limit and to next-to-leading order in the chiral expansion.
The $B\pi$ states are found to typically overestimate the observables at the
few percent level depending on the size of two currently unknown NLO low-energy
coefficients. A strategy to independently measure one of them with the 3-point
function of the light axial vector current will be discussed.
