We present SAFARI, a model checker designed to prove (possibly universally quantified) safety properties of imperative programs with arrays of unknown length. SAFARI is based on an extension of lazy abstraction capable of handling existentially quantified formulæ for symbolically representing states. A heuristics, called term abstraction, favors the convergence of the tool by “tuning” interpolants and guessing additional quantified variables of invariants to prune the search space efficiently.