Five-star Munster down Zebre
Zebre started the match well and looked likely to be the first team to score, but fell behind to Arnold's well-worked first try just before the half-hour.
Brian Scott crossed just before half-time and Guglielmo Palazzani got one back for Zebre for the first score of the second period, before Munster cut loose.
Robin Copeland and Rory Scannell helped bring the bonus point, leaving Arnold to complete his double with the fifth to put the seal on a comfortable win.
The game started with both teams evenly matched and Zebre threatening the Irish province's tryline with a succession of drives inside the first 15 minutes.
The scoreboard remained untroubled throughout the first quarter but on 26 minutes Munster made the breakthrough, with a succession of phases and some neat passing out wide resulting in enough space for Arnold to power over.
10 minutes later and the Limerick-based side had their second try, this time created by a catch-and-drive from a line-out with prop Scott finding himself on the end of it in the corner.
JJ Hanrahan knocked over an expert conversion from the touchline to give the home side a 12-0 lead at the break, with Zebre's Faialaga Afamasaga, unfortunately, seeing his score just before it ruled out for a forward pass.
But Zebre did get their first score on 53 minutes, with good play setting up a scrum five metres out and Palazzani seeking out his way to the line from there.
Zebre's try only seemed to empower the hosts though, and minutes later Munster had their third try after several strong carries up-field, with Copeland dotting down from barely a yard out.
This time it was left to Ian Keatley to add the extras and the Thomond Park outfit wasted no time in securing their crucial fourth try, with Keatley making a superb break to feed Scannell for the score.
There was still time for Arnold to complete his double in the final 10 minutes, with Keatley slotting home the conversion to round off an excellent win.
Tries:Arnold 2, Scott, Copeland, Scannell
Cons: Hanrahan, Keatley 3
Munster: 15 Simon Zebo, 14 Darren Sweetnam, 13 Sammy Arnold, 12 Dan Goggin, 11 Alex Wootton, 10 JJ Hanrahan, 9 Duncan Williams, 8 Robin Copeland, 7 Conor Oliver, 6 Jack O'Donoghue, 5 Billy Holland (captain), 4 Jean Kleyn, 3 Brian Scott, 2 Niall Scannell, 1 James Cronin.
Replacements: 16 Kevin O'Byrne, 17 Jeremy Loughman, 18 John Ryan, 19 Gerbrandt Grobler, 20 Dave O'Callaghan, 21 John Poland, 22 Ian Keatley, 23 Rory Scannell.
Zebre: 15 Ciaran Gaffney, 14 Gabriele Di Giulio, 13 Giulio Bisegni, 12 Faialaga Afamasaga, 11 Giovanbattista Venditti, 10 Serafin Bordoli, 9 Guglielmo Palazzani, 8 Jimmy Tuivaiti, 7 Johan Meyer, 6 Renato Giammarioli, 5 George Biagi (captain), 4 David Sisi, 3 Eduardo Bello, 2 Tommaso D'Apice, 1 Cruze Ah-Nau.
Replacements: 16 Luhandre Luus, 17 Andrea De Marchi, 18 Roberto Tenga, 19 Leonard Krumow, 20 Derick Minnie, 21 Riccardo Raffaele, 22 Maicol Azzolini, 23 Rory Parata.
Referee: Ben Whitehouse (Wales)
Assistant referees: Craig Evans (Wales), Jonny Erskine (Ireland)
TMO: Sean Brickell (Wales)