from tkinter import *
from random import randrange as rnd

root = Tk()
root.geometry('1200x600')
canv = Canvas(root,bg='lightblue')
canv.pack(fill = BOTH, expand = 1)

tail = []
tail_size = 100

x = 0
y = 0
def move(event):
        global x,y
        x = event.x
        y = event.y
 
canv.bind('<Motion>', move)

while 1:
        tail += [(x,y)]
        tail = tail[-tail_size:]
        r = 2
        canv.delete(ALL)
        for t in tail:
                x = t[0]
                y = t[1]
                r += 0.5
                canv.create_oval(x-r//2,y-r//2,x+r//2,y+r//2,fill = 'yellow', width=0)
        canv.update()

mainloop()