A little hard to see, but there's a snake near the center of the photo, which Greg Hunt took today at Powell Island, a part of the marshy area along the Charles in Needham, near the Newton line, just across from Millennium Park in West Roxbury. And he reports it didn't like having its photo taken:
Definitely a rattlesnake as it rattled at us twice before moving along. Didn’t think any were left around Boston outside of the Blue Hills?
Roslindale's resident snake (and turtle) expert, Andrea Howlett, took a look at the photo, though, and said that's no timber rattlesnake, which, yes, inhabits the Blue Hills, but is an eastern milk snake, which also has the ability to rattle, just not to inject poison should it bite.
That is an eastern milk snake. Massachusetts has two non-venomous snakes that will "rattle" their tails if they feel threatened: eastern milk snakes and black racers, both of which can be found in Cutler Park.
It’s thought that this behavior is to distract a potential predator away from their heads, so they can make a quick getaway, although there have been theories that it mimics a rattlesnake.
So your tootsies and chihuahuas are safe along one of the wilder stretches of the Charles, at least until another bobcat returns.