Mobs aren't supposed to be able to pathfind over rails (MC-33359 WAI by Dinnerbone, so I think so they don't interfere with minecarts but I'm not sure), so they will walk around them, but in this case frogs will just jump over them as if they are a full block, which will sometimes cause the frogs to land on the rails

Observed result

Frogs jump over rails and land on them

Expected result

Frogs don't try to jump over rails (as other mobs don't try to jump over rails)

Steps to reproduce

1. Spawn a bunch of frogs in
2. Place a bunch of rails near the frogs
3. Notice the frogs won't pathfind naturally over the rails
4. Notice the frogs sometimes jump over the rails, and will occasionally land on the rails.