Snail trail

When I looked out living room window this morning I was about to cuss the birds for messing on my window till I moved closer and saw this...a blinking big snail. How on earth did it get onto my window?? I watched it on and off but no movement until tonight when it started to rain, see extra blips. I then went to let daft cat out, went into the kitchen and by the time I went back, there was another one half way in over the door. I picked it up put it on the railing. They're everywhere!!!