Leaves on what plant? They do have fluid inside them, otherwise they'd be dead, but I assume you mean bleeding in the way a Ficus does when damaged or cut, but that only happens on certain plants.

some sap in the leaves can be an irritant to the skin and theres one plant --used to be sold as a houseplant not sure it still is-- called dumb cane which if got on the tongue made it swell, most plants are safe but best to know what you are dealing with
but sometimes if the leaves are hydrated they can have a bead of moisture at their tip

If it is a lime tree then their leaves secrete sap which can seriously damage paintwork on houses cars etc by eating into the surface. I know of this to my cost!

Many plants will ooze droplets of dilute sap out of the leaf tips or the tips of the serrations, especially in cool wet weather, and/or with a lot of potassium in the soil. The houseplant Chinese Evergreen (Aglaonema modestum) is notorious for that, and shouldn't be left on an antique table without a nappy!

Tug you should read the Tom duck blog.....and his offspring ;0))