Joseph Gordon-Levitt and Bruce Willis in LooperLOOPER

Rian Johnson's Looper, a time-travel thriller set primarily in the year 2044, casts Joseph Gordon-Levitt as a contract killer whose life is upended with the arrival of his latest target: his older self, who has been transported from the year 2074 and is played by Bruce Willis. This means that, with Gordon-Levitt delivering rather uncanny likenesses of his co-star's traditional scowls and smirks - and with the younger actor's countenance bizarrely altered to resemble the elder actor's familiar face - Willis essentially plays both leading roles ... which isn't the most enticing of setups if, like me, you generally find one Bruce Willis more than enough.

Jerry O'Connell in Piranha 3DPIRANHA 3D

Alexandre Aja's Piranha 3D puts you in the unexpected position of actively rooting for the piranha, not because the effects are all that great (they're actually pretty awful), but because more flesh for the fish means fewer irritating humans to put up with.